Journal Management

ABSTRACT

Apparatuses, systems, methods, and computer program products are disclosed for managing a journal. A method may include reordering storage commands based on different storage volumes associated with the storage commands. A method may include reordering storage commands based on different snapshots associated with the storage commands. A method may include adjusting a frequency of writing data from a write buffer based on a rate of write requests. A method may include adjusting a ratio of storage capacity for storing mirrored write data to storage capacity for storing non-mirrored read data.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/821,201 entitled “PRIMARY DATA STORAGE SYSTEM WITH ADYNAMICALLY TUNABLE JOURNAL” and filed on May 8, 2013 for Kelly E. Long,et al., U.S. Provisional Patent Application No. 61/821,204 entitled“PRIMARY DATA STORAGE SYSTEM WITH A METADATA STRUCTURE FOR FACILITATINGTHE REORDERING OF COMMANDS” and filed on May 8, 2013 for Kelly E. Long,et al., and U.S. patent application Ser. No. 14/273,533 entitled“JOURNAL MANAGEMENT” and filed on May 8, 2014 for Kelly E. Long, et al.,which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure, in various embodiments, relates to a datastorage system suitable for use in a computer network.

BACKGROUND

A computer network may include multiple user computers, a primary datastorage system that stores data provided by the user computers andprovides previously stored data to the user computers, a networkingsystem that facilitates the transfer of data between the user computersand the primary data storage system, or the like. The user computers mayinclude local data storage capacity. In contrast, the primary datastorage system may be separate from the user computers with local datastorage capacity and may provide the ability for the user computers toshare data/information with one another.

The network system between the user computers and the primary datastorage system may take a number of forms. For example, there may be adedicated channel between each of the user computers and the primarydata storage system, the network system may include switches (e.g.,fabric switches) and servers (e.g., initiators) that cooperate totransfer data between the primary data storage system and the usercomputers, or the like.

A secondary data storage system may be associated with a computernetwork. A secondary data storage system may provide secondary storageof data (e.g., storage that is not constantly available for use by oneor more user computers when the computer network is in anormal/acceptable operating mode). As such, a secondary data storagesystem may be employed to backup data and to facilitate othermaintenance functions. In contrast, primary data storage may besubstantially constantly available for use by one or more usercomputers, when the computer network is in a normal/acceptable operatingmode or the like.

SUMMARY

Methods are presented for journal management. In one embodiment, amethod includes receiving a plurality of write commands for differentstorage volumes. A method, in another embodiment, includes adjusting anorder of write commands so that write commands directed to a commonstorage volume are grouped together. In a further embodiment, a methodincludes storing data of the write commands in an adjusted order.

Apparatuses are presented for journal management. In one embodiment, abuffer module is configured to queue input/output (I/O) commandsassociated with different snapshots of a volume. Different snapshots maybe associated with different time periods. An order module, in anotherembodiment, is configured to reorder I/O commands based on whichsnapshot the I/O commands are associated with. In a further embodiment,a journal module is configured to record reordered I/O commands andassociated data in a journal.

An apparatus, in another embodiment, includes means for mirroring cachedwrite data in one or more journals. In a further embodiment, anapparatus includes means for caching read data in at least one journalwithout mirroring the cached read data. An apparatus, in one embodiment,includes means for adjusting a ratio of storage capacity of one or morejournals used for storing mirrored cached write data to storage capacityof the one or more journals used for storing non-mirrored cached readdata based on storage requests for data of the one or more journals.

Computer program products comprising a computer readable storage mediumare presented. In certain embodiments, a computer readable storagemedium stores computer usable program code executable to performoperations for journal management. In one embodiment, an operationincludes monitoring a rate at which write requests are received.

An operation, in a further embodiment, includes increasing a frequencyof writing data from a write buffer to a non-volatile storage medium inresponse to a rate of write requests decreasing. In another embodiment,an operation includes decreasing a frequency of writing data from awrite buffer to a non-volatile storage medium in response to a rate ofwrite requests increasing.

BRIEF DESCRIPTION OF THE DRAWINGS

A more particular description is included below with reference tospecific embodiments illustrated in the appended drawings. Understandingthat these drawings depict only certain embodiments of the disclosureand are not therefore to be considered to be limiting of its scope, thedisclosure is described and explained with additional specificity anddetail through the use of the accompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating one embodiment of anetworked computer system that includes a primary storage system;

FIG. 2 is a schematic block diagram illustrating one embodiment of amanagement stack, an I/O stack, and a fail-over stack;

FIG. 2A is a schematic block diagram illustrating one embodiment of astatistics database;

FIG. 3 is a schematic block diagram illustrating one embodiment of aniSCSI encapsulation packet and an input/out block (IOB) derived from thepacket;

FIG. 4 is a schematic block diagram illustrating one embodiment of avolume ownership table;

FIG. 5 is a schematic block diagram illustrating one embodiment of alayer map and a volume information table;

FIG. 6 is a schematic block diagram illustrating one embodiment ofoperation of a QoS filter of an I/O stack for a primary data storagesystem;

FIG. 7 is a schematic block diagram illustrating one embodiment of ajournal and related journal table;

FIG. 8 is a schematic block diagram illustrating one embodiment of alayer store table;

FIG. 9 is a schematic block diagram illustrating one embodiment of amanagement module;

FIG. 10 is a schematic block diagram illustrating one embodiment ofoperation of a system for journal management;

FIG. 11 is a schematic flow chart diagram illustrating one embodiment ofa method for journal management;

FIG. 12 is a schematic flow chart diagram illustrating a furtherembodiment of a method for journal management; and

FIG. 13 is a schematic flow chart diagram illustrating anotherembodiment of a method for journal management.

DETAILED DESCRIPTION

Aspects of the present disclosure may be embodied as an apparatus,system, method, or computer program product. Accordingly, aspects of thepresent disclosure may take the form of an entirely hardware embodiment,an entirely software embodiment (including firmware, resident software,micro-code, or the like) or an embodiment combining software andhardware aspects that may all generally be referred to herein as a“circuit,” “module,” “apparatus,” or “system.” Furthermore, aspects ofthe present disclosure may take the form of a computer program productembodied in one or more non-transitory computer readable storage mediastoring computer readable and/or executable program code.

Many of the functional units described in this specification have beenlabeled as modules, in order to more particularly emphasize theirimplementation independence. For example, a module may be implemented asa hardware circuit comprising custom VLSI circuits or gate arrays,off-the-shelf semiconductors such as logic chips, transistors, or otherdiscrete components. A module may also be implemented in programmablehardware devices such as field programmable gate arrays, programmablearray logic, programmable logic devices, or the like.

Modules may also be implemented at least partially in software forexecution by various types of processors. An identified module ofexecutable code may, for instance, comprise one or more physical orlogical blocks of computer instructions which may, for instance, beorganized as an object, procedure, or function. Nevertheless, theexecutables of an identified module need not be physically locatedtogether, but may comprise disparate instructions stored in differentlocations which, when joined logically together, comprise the module andachieve the stated purpose for the module.

Indeed, a module of executable code may include a single instruction, ormany instructions, and may even be distributed over several differentcode segments, among different programs, across several memory devices,or the like. Where a module or portions of a module are implemented insoftware, the software portions may be stored on one or more computerreadable and/or executable storage media. Any combination of one or morecomputer readable storage media may be utilized. A computer readablestorage medium may include, for example, but not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, or device, or any suitable combinationof the foregoing, but would not include propagating signals. In thecontext of this document, a computer readable and/or executable storagemedium may be any tangible and/or non-transitory medium that may containor store a program for use by or in connection with an instructionexecution system, apparatus, processor, or device.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++, C#, Objective C, or the like, conventionalprocedural programming languages, such as the “C” programming language,scripting programming languages, and/or other similar programminglanguages. The program code may execute partly or entirely on one ormore of a user's computer and/or on a remote computer or server over adata network or the like.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure. Thus,appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment, but mean “one or more butnot all embodiments” unless expressly specified otherwise. The terms“including,” “comprising,” “having,” and variations thereof mean“including but not limited to” unless expressly specified otherwise. Anenumerated listing of items does not imply that any or all of the itemsare mutually exclusive and/or mutually inclusive, unless expresslyspecified otherwise. The terms “a,” “an,” and “the” also refer to “oneor more” unless expressly specified otherwise.

Aspects of the present disclosure are described below with reference toschematic flowchart diagrams and/or schematic block diagrams of methods,apparatuses, systems, and computer program products according toembodiments of the disclosure. It will be understood that each block ofthe schematic flowchart diagrams and/or schematic block diagrams, andcombinations of blocks in the schematic flowchart diagrams and/orschematic block diagrams, can be implemented by computer programinstructions. These computer program instructions may be provided to aprocessor of a computer or other programmable data processing apparatusto produce a machine, such that the instructions, which execute via theprocessor or other programmable data processing apparatus, create meansfor implementing the functions and/or acts specified in the schematicflowchart diagrams and/or schematic block diagrams block or blocks.

It should also be noted that, in some alternative implementations, thefunctions noted in the block may occur out of the order noted in thefigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. Other steps and methods may be conceived that are equivalentin function, logic, or effect to one or more blocks, or portionsthereof, of the illustrated figures. Although various arrow types andline types may be employed in the flowchart and/or block diagrams, theyare understood not to limit the scope of the corresponding embodiments.For instance, an arrow may indicate a waiting or monitoring period ofunspecified duration between enumerated steps of the depictedembodiment.

In the following detailed description, reference is made to theaccompanying drawings, which form a part thereof. The foregoing summaryis illustrative only and is not intended to be in any way limiting. Inaddition to the illustrative aspects, embodiments, and featuresdescribed above, further aspects, embodiments, and features will becomeapparent by reference to the drawings and the following detaileddescription. The description of elements in each figure may refer toelements of proceeding figures. Like numbers may refer to like elementsin the figures, including alternate embodiments of like elements.

Networked Computer System

With reference to FIG. 1, an embodiment of a networked computer systemthat includes an embodiment of a primary data storage system isillustrated. The networked computer system, hereinafter referred to assystem 20, includes a user level 22, an initiator level 24, a firstswitch level 26 that facilitates communication between the user level 22and the initiator level 24, a primary data storage level 28, a secondswitch level 30 that facilitates communications between the initiatorlevel 24 and the primary data storage level 28, and a secondary datastorage level 32.

A journal in a primary data storage system 28, in one embodiment, is asequenced list of data operations or storage commands (e.g., writecommands, read commands, TRIM commands) that are executed in the orderin which the operations were added to the list. In one embodiment, ajournal or portion of a journal may be stored in a non-volatile memorymedium such as a solid-state storage device 54 or hard disk drive 56. Ina further embodiment, a journal or a portion of a journal may be storedin volatile memory 52. In another embodiment, a first portion of ajournal may be stored in a non-volatile memory medium such as asolid-state storage device 54 or hard disk drive 56 and a second portionof the journal may be stored in volatile memory 52. In certainembodiments, a page or other portion of a journal may be dynamicallypaged or loaded from a solid-state storage device 54 into volatilememory 52, for servicing a read request or the like. A journal maycomprise a sequential log, a circular log, an append-only log, a changelog, a delta log, or other sequenced list. Recording storage commands ina journal, in certain embodiments, allows the storage commands andassociated data to be recovered after a power failure, a system crash,or another restart event.

The present disclosure is directed to a primary data storage system 28that includes a journaling processor (e.g., the management module 900described below) that dynamically tunes a journal. As such, thejournaling processor may assess whether or not to change the currentorder of operations in a journal. More specifically, this assessment maybe based on whether reordering can produce a data space and/ortime-speed benefit relative to a particular data store 48. For example,if the assessment reveals that a sequence of operations would require afirst amount of time to perform on a particular data store 48 but thatreordering the operations such that two operations that were separatedfrom one another by one or more intervening operations now occurred insequence would require a second amount of time that is less than thefirst amount of time, the journaling processor may reorder theoperations. If there is no or little benefit in reordering theoperations, the existing sequence of operations may be maintained.

In one embodiment, the primary data storage system 28 with dynamicallytunable journaling is comprised of: (a) one or more i/o ports, each i/oport capable of receiving a packet with a block command and providing apacket with a reply, (b) a data store system having at least one datastore 48 capable of receiving and storing data in response to a writeblock command and/or retrieving and providing data in response to a readblock command, and (c) a storage processor 46 with a processor andapplication memory for executing computer code, the storage processor 46including a journaling processor for executing computer code related tothe sequencing of the processing of block related commands. Morespecifically, the journaling processor may receive a group of sequencedblock commands, analyze the group of sequenced block commands todetermine whether the sequence of block commands can be reordered toachieve a data space and/or time-speed benefit relative to the datastore, produce a reordered group of block commands if the analysisindicates a data space and/or time-speed benefit can be attained, andadd one of: (i) the reordered group of sequenced block commands and (ii)the group of sequenced block commands to a list of block commands to beexecuted relative to the data store 48. As should be appreciated, theoriginal group of sequenced block commands is added to the list of blockcommands if the analysis did not reveal a meaningful space and/ortime-speed benefit associated with reordering the group of sequencedblock commands.

In another embodiment, the data store system 20 may comprise multipledata stores 48 and the journaling processor operates to analyze whetherthe reordering of block commands for each data store 48 can achieve adata space and/or time-speed benefit relative to the store 48. Inanother embodiment, the data store system 20 comprises multiple datastores 48 and the journaling processor operates to analyze whether thereordering of block commands for a subset of the multiple data stores 48can achieve a data space and/or time-speed benefit for each of the datastores 48 in the subset.

For instance, in one embodiment, two commands in a group of commands maybe separated from one another by several intervening commands, but thesetwo commands may be executed in less time if the group of commands couldbe altered so that these two commands would be executed such that onecommand executes immediately after the other command. This could savetime, for example, in reducing the number and/or extent of a seekoperation required by a disk drive 56 to or from which data is to betransferred.

While the reordering of commands may provide a benefit, the reorderingof commands in a group of commands may also produce different resultsfrom the results that would be obtained if the commands were executed inthe original time sequence order. For instance, if a group of commandsincludes a write command that is followed by a read command and bothcommands relate to the same logical block of data, changing the order ofthe commands such that the read command precedes the write command wouldlikely produce different results. To elaborate, if the commands areexecuted in the original time sequence order, the execution of the readcommand will result in the retrieval of the data that was written inexecuting the write command. In the reordered sequence, execution of theread command will retrieve whatever data was established in the logicalblock prior to the execution of the write command, which is likely to bedifferent from the data that execution of the write command willestablish in the logical block. As such, in certain embodiments, theprimary data storage system 28 may provide the ability to reorder thecommands in a group of commands to obtain a benefit associated with thereordering while also providing the ability to obtain the same resultsas if the commands were executed in the original order. In oneembodiment, the ability to reorder a group of commands but obtainresults as if the original order of the commands was retained isfacilitated using a metadata structure. The extent of the metadatastructure that is employed can vary based upon an analysis of the groupof the commands potentially being reordered, or the like.

User Level. The user level 22 includes at least one user computer thatis capable of being used in a manner that interacts with the primarydata storage level 28. A user computer is capable of requesting that:(a) data associated with the user computer be sent to the primary datastorage level 28 for storage and (b) data stored in the primary datastorage level 28 be retrieved and provided to the user computer. Atleast one user computer associated with the user level is a storageadministrator computer 34 that provides a storage administrator orsystem administrator with the ability to define the manner in which thedata storage provided by the primary data storage level 28 is utilized.As illustrated in FIG. 1, the user level 22 typically includes aplurality of user computers with at least one of the plurality of usercomputers being associated with a storage administrator and the otheruser computers being associated with other entities. For the purpose ofillustration, the user level 22 includes user computers 36A-36Crespectively associated with a customer support department, anaccounting department, and an engineering department.

Initiator Level. The initiator level 24 includes at least one initiatorthat operates to translate a request from a user computer into one ormore block command packets. A request from a user computer is in theform of a request packet that conforms to a packet protocol such as TCP,IP, Web, DB, and FileShare. A block command packet conforms to a blockprotocol that includes block commands for data storage devices thatoperate on one or more blocks of data. Examples of block protocols arethe Internet Small Computer System Interface protocol (iSCSI), the FiberChannel protocol (FC), TCP, and IP. Examples of block commands include:(a) a block write command that directs a data storage device to writeone or more blocks of data to storage media associated with the deviceand (b) a block read command that directs a data storage device to readone or more blocks of data from a storage media associated with thedevice. A block of data is a fixed and predetermined number ofcontiguous bytes of data that is or will be resident on some kind ofstorage media. Typical block sizes are 512, 1024, 2048, and 4096 bytes.For example, a request from a user computer to read a large file of dataresident at the primary data storage level 28 is likely to be translatedby an initiator into multiple block command packets that each relate toone or more blocks of data that is/are part of the requested file.

The initiator also operates to translate a block result packet, a packetthat is received by the initiator and provides the result or a portionof the result of the execution of a block command associated with ablock command packet, into a reply to request packet. The initiatorprovides the reply to the request packet to the appropriate usercomputer.

As illustrated in FIG. 1, the initiator level 24 commonly includes aplurality of initiators with each of the initiators capable of: (a)processing request packets from each of the user computers to generateblock command packets and (b) processing block result packets to producereply to request packets that are provided to the appropriate usercomputers. For the purpose of illustration, the initiator level includesinitiators 38A-38C.

An initiator can be comprised of a cluster of two or more computers thateach endeavors to process a request from a user computer and thatprovide redundancy in the event that one or more of the computers fail.Typically, an initiator that is designated to process high priority orcritical requests is comprised of multiple computers, thereby providingredundancy should any one of the computers fail.

First Switch Level. The first switch level 26 provides the ability forone or more user computers at the user level 22 to communicate with oneor more initiators at the initiator level 24. More specifically, thefirst switch level 26 operates so as to receive a request packet from auser computer, process the request packet to determine which initiatorshould receive the request packet, and routes the request packet to theappropriate initiator. Conversely, the first switch level also operatesto receive a reply to request packet from the initiator level 24,process the reply to request packet to determine which user computershould receive the reply to request packet, and routes the reply torequest packet to the appropriate user computer.

The first switch level 26 can include a single switch that connects oneor more user computers to one or more initiators or multiple switchesthat each connects one or more user computers to one or more initiators.For the purpose of illustration, the first switch level 26 includes aswitch 40 that is capable of establishing communication paths betweenthe user computers 34 and 36A-36C and the initiators 38A-38C.

Primary Data Storage Level. The primary data storage level 28 (orprimary data storage system 28) operates to receive a block commandpacket from an initiator, attempt to execute the block command containedin the block command packet, produce a block result packet that containsthe result of the attempted execution or execution of the block command,and provide the block result packet to the initiator that sent therelated block command packet to the primary data storage system 28.

Typical block commands include a write command and a read command. Inthe case of a write command, the primary data storage system 28 attemptsto write one or more blocks of data to a data store (sometimes referredto simply as a “store”) associated with the primary data storage system28. With respect to a read command, the primary data storage system 28attempts to read one or more blocks of data from a data store associatedwith the primary data storage system 28 and provide the read data to theinitiator.

The primary data storage system 28 includes at least one storageprocessor and at least one data store. The primary data storage system28 also includes at least one switch when the at least one storageprocessor and the at least one data store associated with the at leastone storage processor will accommodate two or more independentcommunication paths between the at least one storage processor and theat least one data store.

A storage processor includes an application memory and a processor forexecuting code resident in the application memory to process a blockcommand packet. In one embodiment, the processor and the applicationmemory are embodied in a SuperMicro Superserver 6036ST.

A data store is (a) a single data storage device or element or (b) acombination of data storage devices or elements. Examples of a singledata storage element that can each be a data store include a CPU busmemory, a disk drive with a magnetic/optical disk, a solid state drive,and a tape drive with a tape. An example of a combination of datastorage devices or elements that are configured to operate as a singledata store is a group of disk drives configured as a Redundant Array ofIndependent Drives or RAID.

A data store can be characterized by the attributes of path redundancy,data redundancy, and persistence.

The path redundancy attribute is a measure of the number of redundantand independent paths that are available for writing data to and/orreading data from a data store. As such, the value of the pathredundancy attribute is the number of independent paths (e.g., theindependent I/O ports associated with the data store) less one. Thevalue of the path redundancy attribute is one or greater when there areat least two independent paths available for writing data to and/orreading data from the data store. If there is only one independent pathavailable for writing data to and/or reading from a data store, the pathredundancy is zero.

The data redundancy attribute is a measure of the number of failures ofelements in a data store that can be tolerated without data loss. Assuch, the value of the data redundancy attribute is the number ofelements in the data store less the number of elements that can failbefore there is data loss. For example, if a data store is comprised oftwo disk drives (elements) with the data on one disk drive mirroring thedata on the other disk drive, the value of the data redundancy attributeis one because the failure of one disk drive means that the data canstill be recovered but the failure of both disk drives would mean thatthere would be data loss. As another example, the value of the dataredundancy attribute of a RAID-6 data store comprised of six disk drives(elements) is two because the two of the disk drives (elements) can failand the data can still be recovered but the failure of three or moredisk drives (elements) would preclude the recovery of the data.

The persistence attribute is an indication of: (a) the presence of dataon a data store for a substantial period of time without power beingapplied to the data store or (b) data remaining on a data store for asubstantial period of time due to the presence of a primary power sourceand an independent backup power source that operates in the event of thefailure of the primary power source. For example, if a data store is asingle magnetic disk drive, the persistence attribute is “positive”because data will remain on the magnetic disk drive for a substantialperiod of time in the absence of power being applied to the drive. Incontrast, a data store that is volatile memory without battery backuphas a persistence attribute that is “negative” because data establishedin the memory will not remain in the memory in the absence of powerbeing applied to the memory.

A data store also provides at least one of a number of possiblecombinations of read and write operations, including read-only, read andwrite, write-only, and write-once-read-many (WORM).

The switch facilitates communications between each of the storageprocessors or a subset of all of the storage processors associated withthe primary data storage level 28 and each port of all of the datastores associated with the primary data storage system 28 or a subsetthereof.

In many situations, redundancy that allows the primary data storagesystem 28 to continue operation in the event of a predetermined level offailure of a storage processor, an element of a data store, and or aswitch is desired. This redundancy refers to path redundancy in whichthere are at least two separate and independent paths extending at leastpart of the way between an I/O interface of the primary data storagesystem 28, the interface that initially receives a block command packetfrom an initiator and from which a block result packet is transmitted toan initiator, and a data store.

To provide one embodiment of path redundancy, the primary data storagesystem 28 includes: (a) an I/O interface 42 comprised of network cards44A-44D, (b) first and second storage processors 46A, 46B, (c) first andsecond data store systems 48A, 48B, and (d) first and second switches50A, 50B. It should be appreciated that storage processors 46A, 46Bcould each be a single processor or multiple processors operatingcohesively.

The network cards 44A-44D (sometimes referred to as “Ethernet cards”) ofthe I/O interface 42 are each addressable by one or more of whateverinitiators are operative at the initiator level 24. In the illustratedembodiment, each of the network cards 44A-44D is an Ethernet card thatis appropriate for use when all of the initiators that are active at theinitiator level 24 are conducting communications with the primary datastorage system 28 pursuant to the Ethernet protocol. Other cards can beemployed if a different protocol, such as Fibre Channel, is used by theinitiators.

The first and second data store systems 48A, 48B are each comprised of aportion of a data store, a portion of each of multiple data stores, adata store, multiple data stores, or combinations thereof.

The first and second switches 50A, 50B each provide at least a portionof the ability to connect (a) one or more of the network cards 44A-44Dto a selected one of the storage processors 46A, 46B, (b) first andsecond storage processors 46A, 46B to one another, and (c) a selectedone of the storage processors 46A, 46B to a selected one of the firstand second data store systems 48A, 48B. The ability of switch 50A toestablish a connection to a store in the data store system 48B dependson the store having at least one of two input/output ports available forestablishing a connection with the switch. Similarly, the ability ofswitch 50B to establish a connection to a store in the data store system48A depends on the store having one or at least two input/output portsavailable for establishing a connection with the switch.

The path redundancy that is provided by the embodiment of the primarydata storage system 28 shown in FIG. 1 contemplates the failure of: (a)one or more but less than all of the Ethernet cards 44A-44D, (b) one ofthe first and second storage processors 46A, 46B, (c) one of the firstand second switches 50A, 50B, and/or (d) a data store associated withone of the first and second data store systems 48A, 48B.

To elaborate, partial path redundancy is provided by rendering at leasttwo of the network cards 44A-44D with the same initiator. If one of theat least two Ethernet cards fails, the other operative Ethernet card(s)provide(s) path redundancy for the initiator.

Partial path redundancy is provided by the two storage processors 46A,46B. If one of the first and second storage processors 46A, 46B fails,the other storage processor can be utilized to provide the pathredundancy between the I/O interface 42 and a data store. In thisregard, the non-failing storage processor may use one or both of theswitches 50A, 50B. For example, if the storage processor 46A isexclusively responsible for communications conducted over Ethernet card44A, storage processor 46A needs to process a command propagated overEthernet card 44A and associated exclusively with the first data storesystem 48A, and storage processor 46A fails, the storage processor 46Bcan utilize both the first and second switches 50A, 50B to complete acommunication path between the Ethernet card 44A and the first datastore system 48A, e.g., the storage processor 46B utilizes the first andsecond switches 50A, 50B to communicate with both the Ethernet card 44Aand the first data store system 48A.

Partial path redundancy is provided by the first and second switches50A, 50B. If one of the first and second switches 50A, 50B fails, theother switch can be utilized to provide the necessary path redundancy.This path redundancy is dependent upon the non-failing switch having:(a) access to a portion of the data store that provides data redundancyrelative to the portion of the data store that is no longer accessibledue to the failure of the other switch and (b) access to an Ethernetcard that can be addressed by the same initiator as the Ethernet card(s)that is/are no longer available due to the failure of the other switch.For example, if Ethernet cards 44A and 44C are each addressable by thesame initiator, the data store systems 48A and 48B each include anelement that together define a data store in which one element mirrorsthe other element, and switch 50A fails, the switch 50B can be utilizedto establish the necessary communication between the Ethernet card 44Cand the element in data store system 48B.

Additionally, in many situations, multiple data stores that havedifferent storage characteristics (e.g., speed, capacity, redundancyand/or reliability) are desired. In this regard, the first data storesystem 48A is comprised of: (a) a first data store that is a first CPUbus memory 52A (sometimes referred to as memory store 52A) and isrelatively fast but with relatively low capacity and no redundancy, (b)a second data store that is a first solid state disk or drive (SSD) 54Awith less speed but greater capacity relative to the first CPU busmemory 52A and no redundancy, and (c) a third data store in the form ofa first RAID disk array 56A with less speed and greater capacity thanthe first solid state disk 54A and redundancy. CPU bus memory is memorythat is accessible to a processor of a storage processor via theprocessor's address bus, available for use by the processor, useable bythe processor in processing a block command packet, and does not containany portion of the application program that is executed or could beexecuted in the processing of a block command packet. In contrast, theprocessor accesses the first SSD 54A and the first RAID disk array 56Avia an expansion bus (e.g., PCIe). Relatedly, stores having similarcharacteristics are typically configured within a primary data storagesystem so as to constitute a tier.

It should be appreciated that the first data store system 48A can becomprised of other combinations of partial data stores and/or datastores. For instance, the first data store system 48A could include afirst disk drive and the second data store system 48B could include asecond disk drive, the first and second disk drives together forming adata store in which the first and second disk drives mirror one anotherto provide data redundancy. In the illustrated embodiment, the seconddata store system 48B includes data stores in the forms of a second CPUbus memory 52B (sometimes referred to as memory store 52B), a second SSD54B, a second RAID disk array 56B. It should be appreciated that thesecond data store system 48B can also include other combinations of datastores and partial data stores.

In a data store system that includes CPU bus memory and non-CPU bus datastorage, the switch that is used to establish connections between theprocessor of a storage processor and the data store system is comprisedof a type A switch that establishes connections with the non-CPU busdata storage and a type B switch that establishes connections with theCPU bus memory.

Because the first and second data store systems 48A, 48B respectivelyinclude CPU bus memories 52A, 52B, the first and second switches 50A,50B respectively include type B switches 60A, 60B that respectivelyallow the processors of the storage processors 46A, 46B to establishcommunication paths with the CPU bus memories 52A, 52B. A type B switchis comprised of the hardware, software, and/or firmware associated witha storage processor that allow the processor to access the memorylocations on the CPU memory bus associated with the CPU bus memory.

Further, because the first and second data store systems 48A, 48Brespectively include non-CPU bus data storage in the form of SSD and SASdevices, the first and second switches 50A, 50B respectively includetype A switches 58A, 58B that respectively allow the processors of thestorage processors 46A, 46B to establish communication paths with thenon-CPU bus data stores. A type A switch is comprised of the hardware,software, and/or firmware associated with an expansion bus that allowsthe processor to access the data on the non-CPU bus data storages. Incertain embodiments, the primary data storage system 28, the one or moredata stores 48, or the like comprise a storage appliance (e.g., anetwork storage appliance, a storage area network (SAN) storageappliance, network-attached storage (NAS), or the like). A storageappliance, as used herein, comprises a specialized computing deviceconfigured to provide access to a data store 48 over a network orfabric, with or without a dedicated host device.

Second Switch Level. The second switch level 30 provides the ability foreach of the initiators associated with the initiator level 24 tocommunicate with at least one network card associated with the primarydata storage system 28, the at least one network card being associatedwith at least one storage processor of the primary data storage system28. More specifically, the second switch level 30 operates to receive ablock command packet from an initiator and process the block commandpacket so as to route the packet to the address that is associated witha particular network card. Conversely, the second switch level 30 alsooperates to receive a block result packet from the primary data storagesystem 28 and process the block result packet so as to route the packetto the appropriate initiator.

The second switch level 30 can include a single switch that selectivelyconnects one or more initiators to one or more network cards or multipleswitches that each selectively connects one or more initiators to one ormore network cards. For the purpose of illustration, the second switchlevel 30 includes switch 61 that is capable of selectively establishinga communication path between each of the initiators 38A-38C and each ofthe network cards 44A-44D.

Secondary Data Storage Level. The secondary data storage level 32provides secondary storage of data, e.g., storage that is not constantlyavailable for use by one or more user computers when the system 20 is ina normal/acceptable operating mode. In contrast, primary data storage issubstantially constantly available for use by one or more user computerswhen the system 20 is in a normal/acceptable operating mode. Thesecondary data storage level 32 can include many different types of datastorage, including tape drives, robotic data storage systems that employrobots to move storage media between players/recorders and storagelocations, “cloud” storage etc. It should be appreciated that thesetypes of data storage and other types of data storage that are largelyused as secondary data storage can, in appropriate circumstances, becomeprimary storage.

The secondary data storage level 32 includes a backup/tape server 62that communicates with one or more of the initiators at the initiatorlevel 24 in response to a request packet issued by a user computer atthe user level 22.

The secondary data storage level 32 also includes a cloud storageprovider 64 that is accessible to the primary data storage system 28. Inthe illustrated embodiment, the cloud storage provider 64 can be a partof a data store, part of multiple data stores, a data store, multipledata stores, or combinations thereof that is respectively accessible tothe storage processors 46A, 46B via network cards 66A, 66B (which areEthernet cards in the illustrated embodiment) and the type A switches58A, 58B respectively associated with switches 50A, 50B.

System Administrator Communication Path. The system administratorcomputer 34 communicates with the primary data storage system 28 and,more specifically, the storage processor(s) in the primary data storagesystem 28 to define the manner in which the data storage provided by theprimary data storage system 28 can be utilized. The communication pathbetween the system administrator computer 34 and a storage processor inthe primary data storage system 28 is from the system administratorcomputer 34 to the switch 40 and from the switch 40 to a network card.The network card and the storage processor can be connected to oneanother via the switch in the primary data storage system 28 thatservices the network cards associated with the initiators.

In the illustrated embodiment, the system administrator computer 34respectively communicates with the storage processors 46A, 46B vianetwork cards 68A, 68B and switches 50A, 50B.

It should be appreciated that the administrator computer 34 can alsocommunicate with the storage processors 46A, 46B via one or more pathsthat include the first switch level 26, the initiator level 24, and thesecond switch level 30.

Primary Data Storage Level Communications

The primary data storage system 28 receives and processes two types ofcommunications. The first type of communications is administratorcommand packets related communications. Administrator command packetsare processed using a management stack. The second type ofcommunications is block command packets that relate to the writing ofdata to a data store or the reading of data from a data store. Blockcommand packets are processed using an IO stack.

With reference to FIG. 2, the administrator command packets areprocessed using a management stack 100. There is a management stack 100associated with each storage processor at the primary data storagesystem 28. The management stack 100 is embodied in software that isexecuted by the storage processor. Generally, the management stack 100operates to receive an administrator command packet that relates to theprimary data storage system 28, processes the administrator commandpacket, and provides a reply packet, if appropriate. The receiving,processing, and replying of an administrator command packet by themanagement stack 100 involves interaction with other software elementsand hardware elements within the primary data storage system 28. Amongthe software elements with which the management stack interacts are: anIO stack and, if there is another storage processor, a fail-over managerand a second management stack. An example of a hardware element thatinteracts with the management stack 100 is a network card. In addition,the management stack 100 operates to conduct communications with anyother storage processors at the primary data storage system 28.

With continuing reference to FIG. 2, the block command packets areprocessed by an IO stack 102. An IO stack 102 is associated with eachstorage processor at the primary data storage system 28. Generally, theIO stack 102 operates to receive a block command packet that relates tothe primary data storage system 28, processes the block command packet,and provides a result packet if appropriate. The process of receiving,processing, and replying of a block command packet by the IO stack 102involves interaction with other software elements and hardware elementswithin the primary data storage system 28. Among the software elementswith which the IO stack 102 interacts are: the management stack 100 and,if there is another storage processor, the fail-over manager associatedwith the other storage processor. An example of a hardware element thatinteracts with the IO stack 102 is a network card.

The IO stack 102 also communicates with a fail-over manager 104. Ifthere is more than one storage processor at the primary data storagelevel 28, there is a fail-over manager 104 associated with each storageprocessor. Generally, the fail-over manager 104 operates to: (a)initiate a request from the “home” storage processor (e.g., the storageprocessor with which the fail-over manager is associated) to a “foreign”storage processor (e.g., a storage processor other than the “home”storage processor) to transfer responsibility for a logical unit number(LUN) or volume to the “foreign” storage processor and (b) facilitatethe processing of a request from a “foreign” storage processor totransfer responsibility for a volume to the “home” storage processor. Avolume, as used herein, may comprise a logical or physical unit orgrouping of storage, memory, and/or data. A LUN or volume may be alogical or physical unit of storage within the data store(s) 48 providedby the primary data storage system 28. A volume may comprise a portionof a data store 48; a portion of each of multiple data stores 48A, 48B;a data store 48; multiple data stores 48A, 48B; or combinations thereof.A volume may comprise a storage volume, a logical volume, a physicalvolume, or another logical or physical container for data.

Management Stack

The management stack 100 operates to: (a) receive an administratorcommand packet (b) communicate with the block processing stack to theextent necessary to process an administrator command packet, and (c)transmit a reply packet directed to the administrator computer 34 to theextent the processing of an administrator command packet requires areply. Examples of administrator command packets include packets thatrelate to the creation of a LUN/volume within the primary data storagesystem 28, the assignment of Quality-of-Service (QoS) goals for aLUN/volume, the association of a LUN/volume with an initiator, theconfiguration of a network card (e.g., the assigning of an address tothe Ethernet card so that the card is available to one or moreinitiators), requesting of data/information on the operation of aLUN/volume, the destruction of a LUN, and maintenance operations.

The management stack 100 conducts communications with the IO stack 102that relate to a volume(s) for which the IO stack 102 is responsible.Among the communications with the IO stack 102 are communications thatinvolve the creation of a volume, the assignment of QoS goals to avolume, the association of a volume with an initiator, the configurationof an network card, the acquisition of data/information relating to avolume or volumes for which the IO stack 102 is responsible, and thedestruction of a volume.

The management stack 100 is also capable of communicating with afail-over manager 104 via the IO stack 102. For example, if anadministrator wants to temporarily disable the IO stack 102 to updatethe IO stack 102 but does not want to disable one or more of the volumesfor which the IO stack 102 is responsible, an administrator commandpacket can be issued to implement an administrator fail-over in whichthe management stack 100 communicates with the fail-over manager 104 viathe IO stack 102 to transfer responsibility for the relevant volumes toanother storage processor in the primary data storage system 28.

The management stack 100 is also capable of communicating with themanagement stacks associated with other storage processors at theprimary data storage system 28 to facilitate coordination between thestorage processors. For example, the management stack 100 communicatesvolume creation/destruction, changes in QoS for a volume, network cardaddress changes, administrator identification and password changes, andthe like to the management stacks associated with other storageprocessors in the system.

The management stack 100 is comprised of: (a) an Ethernet hardwaredriver 108, a TCP/IP protocol processor 110, a Web protocol processor112 and/or a Telnet protocol processor 114, a JavaScript Object Notation(JSON) or Jason parser 116, a Filesystem in Userspace (FUSE) 118, amanagement server 120, and a management database 122.

The Ethernet hardware driver 108 controls an Ethernet card so as toproduce the electrical signals needed to receive a message, such as anadministrator command packet, and transmit a message, such as replypacket. The TCP/IP protocol processor 110 at the TCP level manages thereassembly (if needed) of two or more packets received by an Ethernetcard into the original message (e.g., an administrator command packet)and the disassembly (if needed) of a message into two or more packetsfor transmission (e.g., a reply to an administrator command).

The TCP/IP protocol processor 110 at the IP level assures the addressingof packets associated with a message. With respect to received packets,the IP level confirms that each of the received packets does, in fact,belong to the IP address associated with the Ethernet card. With respectto packets that are to be transmitted, the IP level assures that theeach packet is appropriately addressed so that the packet gets to thedesired destination. With respect to a received message, the TCP levelalso recognizes the packet as requiring further routing through themanagement stack 100, e.g., to the Web protocol processor 112 or Telnetprotocol processor 114. The TCP/IP protocol processor 110 also performsother processing in accordance with the protocols, e.g., orderingpackets, checksum etc.

The Web protocol processor 112 is used when the administrator computer34 is employing a browser to interact with the management stack of theprimary data storage system 28. The Web protocol processor 112 includesa Hyper Text Transport Protocol (HTTP) daemon that receives a message(e.g., an administrator command packet) and processes the message bypassing the message on to the JSON parser 116. Subsequently, the daemonis informed by the JSON parser 116 of any reply to the message andpasses the reply (Web pages etc.) on up to the TCP/IP protocol processor110 for further processing.

As an alternative to the Web protocol processor 112, a Telnet protocolprocessor 114 can be utilized. The Telnet protocol processor 114includes a daemon that receives a message (e.g., an administratorcommand packet) and processes the message by passing the message on tothe JSON parser 116. Subsequently, the daemon is informed by the JSONparser 116 of any reply to the message and passes the reply on up to theTCP/IP protocol processor 110 for further processing.

The JSON parser 116 serves as a translator between the Web protocolprocessor 112 (and Telnet protocol processor 114 or most other similartypes of protocol processors) and the FUSE 118 and management server120. More specifically, the JSON parser 116 operates to translatebetween “Web language” and JSON language. Consequently, the Jason parser116 translates an administrator command packet received from the Webprotocol processor 112 into JSON language. Conversely, the Jason parser116 translates a reply to an administrator command from JSON languageinto Web language for passing back up the management stack. Thetranslation of “Web” language” into JSON language produces a file call,e.g., a request relating to a particular file.

The FUSE 118 is a loadable kernel module for Unix-like operating systemsthat allows the creation of a file system in a userspace program. TheFUSE 118 serves as an application program interface (API) to the filesystem in the management server 120, a portion of the userspace program.More specifically, the FUSE 118 operates to receive a file call from theJSON parser 116, convey the file call to the management server 120,receive any reply to the file call generated by the management server120, and convey any reply to the JSON parser 116 for further conveyanceup the management stack. The context of the file call indicates the filewithin the management server that is to be executed, e.g., a volumecreation or a volume destruction.

The management server 120 operates to: (a) receive a file call from theFUSE 118 that is representative of an administrator command embodied inan administrator command packet, (b) execute the file that is thesubject of the file call, and (c) communicate the result of the executedfile to the FUSE 118 for further conveyance up the management stack,typically this results in the administrator computer 34 being providedwith a new or updated Web page with an update as to the status of theexecution of the administrator command, e.g., the command executed orthe command failed to execute.

The file that is the subject of the file call can result in themanagement server 120 communicating with the IO stack 102, the fail-overmanager 104, the management database 122, and/or another storageprocessor. For example, if the goal of the file to be executed is thecreation of a volume, in executing the file, the management server 120will communicate with the IO stack 102, the fail-over manager 104, themanagement database 122, and other storage processors. As anotherexample, if the goal of the file to be executed is to provide theadministrator computer 34 with statistics relating to a particularvolume, in executing the relevant file, the management server 120 willcommunicate with the IO stack 102 to obtain the necessary statistics onthe particular volume.

The management server 120, in addition to processing administratorcommand packets that propagate down the management stack, also processescommands or requests for information from management servers associatedwith other storage processors. For instance, a “foreign” managementserver that is associated with a different storage processor than themanagement server 120 may have processed an administrator command packetsetting forth a new administrator id/password. The foreign managementserver would update its management database and forward a command to themanagement server 120 to update the management database 122 with the newadministrator id/password.

The management database 122 has three portions: (a) a local objectportion to which only the management server 120 can read/write, (b) ashared object portion to which the management server 120 can read/writebut can only be read by another management server, and (c) a sharedobject to which the management server 120 can read/write and to whichanother management server can read/write. An example of a shared objectto which the management server 120 can read/write but that can only beread by another management server is information that is specific to thestorage processor with which the management server 120 is associated,e.g., CPU usage or CPU temperature. An example of a shared object towhich both the management server 120 and another management server canread/write is an administrator id/password.

IO Stack

FIG. 2 illustrates the IO stack 102, e.g., a group of processes that areexecuted by each storage processor associated with the primary storagelevel 28 in processing a block command packet relating to a particularblock of data or multiple blocks of contiguous data.

Generally, the IO stack 102 is comprised of network protocol processors130 (sometimes referred to as “network processors”) that conduct theprocessing needed to conduct communications with other elements in acomputer network according to various network protocols and a filterstack 132 that process block commands so as to read data from and writedata to a data store associated with the primary data storage system 28.

Network Protocol Processors.

iSCSI. A SCSI block command can be conveyed to the primary data storagesystem 28 over an Ethernet and according to Internet protocols, e.g.,according to iSCSI protocols. The SCSI block command is embedded in ablock command packet that conforms to the iSCSI protocols. In such asituation, the network protocol processors 130 includes the Ethernethardware driver 108, the TCP/IP protocol processor 110, and an iSCSIprotocol processor 140 for processing the block command packet with theSCSI block command. Generally, the Ethernet hardware driver 108 and theTCP/IP protocol processor 110 operate as previously described withrespect to the management stack 100. In this instance, however, the TCPlayer of the TCP/IP protocol processor 110 recognizes that the receivedpacket as a block command packet and not an administrator commandpacket. Moreover, the TCP layer recognizes the block command packet ashaving an iSCSI block command. As such, the block command packet isrouted by the TCP/IP protocol processor 110 to the iSCSI protocolprocessor 140 for further processing. The iSCSI protocol processor 140operates to assure that the iSCSI portion of a received block command isin conformance with the iSCSI standard. If the iSCSI portion of a blockcommand packet is in conformance, the block command is passed on to thefilter stack 132. The Ethernet hardware driver 108, TCP/IP protocolprocessor 110, iSCSI protocol processor 140, also process any resultpacket (e.g., a packet that conveys the result of the execution of aSCSI block command or failure to execute a SCSI block command) forforwarding to the initiator that originated the block command packet.

FibreChannel. A SCSI block command can also be conveyed over a FibreChannel (FC) network and according to Fibre Channel protocols. The SCSIblock command is embedded in a block command packet that conforms to theFC protocol. In such a situation, the network protocol processors 130include a FC hardware driver 150 and a FC protocol processor 152. The FChardware driver 150 operates to control a Fibre Channel card (whichreplaces the Ethernet card, e.g., Ethernet cards 44A-44D) so as toproduce the electrical signals needed to receive a block command packetthat conforms to the FC protocols and transmit a result packet to theinitiator that originated a block command packet. The FC protocolprocessor 152 (a) manages the reassembly (if needed) of two or morepackets received by a Fibre Channel card into the original block commandpacket and the disassembly (if needed) of a result packet into two ormore packets for transmission, and (b) assures the addressing of packetsassociated with a received block command packet and associated with areply packet.

Fibre Channel over Ethernet (FCoE). A SCSI block command can also beconveyed over an Ethernet and according to Fibre Channel protocols. TheSCSI block command is embedded in a block command packet that conformsto the Ethernet and FC protocol. In such a situation, the networkprocessors 130 include the Ethernet hardware driver 108 and the FCprotocol processor 152.

It should be appreciated that the primary data storage system 28operates to process block commands, e.g., commands that relate to thereading of a block data from or writing of a block data to a storagemedium. As such, the primary data storage system 28 can be adapted tooperate with block commands other that SCSI commands.

Further, the primary data storage system 28 can be adapted to processblock commands regardless of the type of network used to convey theblock command to the primary data storage system 28 or to transmit thereply to a block command from the primary data storage system 28. Assuch, the primary data storage system 28 can be adapted to operate withnetworks other than Ethernet and FC networks.

Moreover, the primary data storage system 28 can be adapted to operateon block commands that are conveyed over a network according toprotocols other than Ethernet, TCP/IP or FC.

Filter Stack.

The filter stack 132 is comprised of a target driver filter 160, a groupof foreground filters 162, and a group of background filters 164.Associated with the filter stack 132 are a filter manager 166 and astatistics database 168. Operations that involve executing or attemptingto execute a SCSI block command flow “down” the stack, e.g. in thedirection going from the target driver filter 160 and toward the groupof background filters 164. In contrast, operations that involvegenerating or providing the result of the execution or attemptedexecution of a SCSI block command flow “up” the stack. Consequently, afilter involved in executing or attempting to execute a SCSI blockcommand may also be involved in generating or providing the result ofthe execution or attempted execution of the SCSI block command.

Generally, the target driver filter 160 processes block command packetto generate an input/output block (IOB) that is used by the otherfilters to store data/metadata relating to the processing of a blockcommand. As such, the IOB facilitates the communication of data/metadatabetween filters. The IOB that is initially generated by the targetdriver filter 160 flows down the filter stack 132 and is on occasionreferred to as command IOB. After there is a result relating to a SCSIblock command associated with an (execution or failure to execute), theIOB flows up the stack and is on occasion referred to as a result IOB.The target driver filter 160 also operates to generate a result packetfrom a received result IOB and passes the result packet on up the stackto the network processors 130.

Generally, the group of foreground filters 162 process a command IOB to:(a) cause whatever write/read related operation is required of a blockcommand to occur and (b) cause one or more tasks needed to accomplishthe read/write operation to occur in a fashion that endeavors to meetQoS goals. The foreground filters 162 also process a result IOB asneeded and provide the result IOB to the target driver filter 160.

Generally, the group of background filters 164 cause one or more tasksrelated to administrator defined QoS goals to occur and that, ifperformed in the foreground process, would significantly impact theability to meet QoS goals.

Generally, the filter manager 166 operates to create (associate) thefilter stack 132 with a volume (an identifiable unit of data storage),destroy (disassociate) a volume from the filter stack 132, andcooperates with the fail-over manager 104 and/or management server 120to implement various volume related functions (e.g., using themanagement server 120 to inform “foreign” storage processors of thecreation of a new volume).

The statistics database 168 receives statistical data relating to avolume from one or more filters in the filter stack 132, stores thestatistical data, consolidates statistical data based upon data providedby a filter, stores calculated statistical data, and provides the storedstatistical data to one or more filters in the filter stack 132 and tothe management server 120.

Generally, the filter manager 166 operates to create (associate) thefilter stack 132 with a volume (an identifiable unit of data storage),destroy (disassociate) a volume from the filter stack 132, andcooperates with the fail-over manager 104 and/or management server 120to implement various volume related functions (e.g., using themanagement server 120 to inform “foreign” storage processors of thecreation of a new volume). To elaborate with respect to the creation ofa volume, the filter manager 166 receives a message from the ManagementServer 120 instructing filter manager 166 to create a new volume with aspecific filter stack configuration. The filter manager 166 instantiatesthe filters and places them in the correct hierarchy based on thestorage administrator request. For example, with respect to FIG. 2, thefilter manager creates an instance of target driver 160 and IO forwardfilter 270 and ensures that target driver 160 sends IOBs “down” thestack to the IO Forward filter 270. Similarly, filter manager 166creates, configures, and connects the rest of the filter stack 132. Toelaborate with respect to the deletion of a volume, the filter manager166 unlinks the connections and removes each of the filters in thestack.

Statistics Database. The statistics database 168 receives data fromvarious hardware and software elements within the system and providesdata to many of the elements within the system that use the data inmaking one or more decisions relating to a data storage operation. Dueto the extensive use of the statistics database 168 throughout thesystem, a description of the database 168 is provided prior to thedescriptions of the various IO filters, many of which make use of thedatabase. Initially, it should be appreciated that the structure of thestatistics database 168 can vary based upon the hardware and softwareelements present in the system. Further, the statistics database canstore data that is derived from data provided by a single element orfrom data provided by multiple elements. Consequently, the statisticsdatabase 168 can be quite extensive.

With reference to FIG. 2A, an example of a portion of a statisticsdatabase 258 is described to facilitate the understanding of the use ofthe database 168 by various filters. With respect to the example of aportion of the statistics database 258, it should be appreciated that aportion of the database relates to hardware. In this case, the portionthat relates to hardware includes statistics relating to a CPU, aSolid-State Disk (SSD), and an Ethernet card. A portion of the exampleof a portion of the statistics database 258 relates to volume relateddata. In this case, the portion that relates to volume data includesstatistics directed to three different criticalities, a volume, and aninitiator. With respect to both the hardware and volume statistics,statistic relating to throughput, queue depth, latency, and use countare provided. The use count with the “second” resolution corresponds toIOPS. The use count with respect to resolutions of greater duration areIOPS scaled to the resolutions of the greater duration. Additionally,with respect to each of throughput, queue depth, latency, and use count,statistics are provided in terms of both reads and writes. Further, itshould be appreciated that the example of a portion of a statistics dataincludes current statistical data and historical statistical data. Thecurrent statistical data has a resolution of “second.” The historicalstatistical data has resolutions great than “second” and includeresolutions of “minute”, “hour”, and “day”. It should be appreciatedthat only one resolution of current statistical data and one resolutionof historical statistical data can be utilized, provided the resolutionassociated with the historical statistical data is for a greater periodof time than the resolution associated with the current statisticaldata. It should also be appreciated that resolutions other than thoseshown can be utilized. It should also be appreciated that a morecomplete example of the statistics database would likely includestatistical data relating to additional volumes and additional hardwarecomponents (e.g. SAS, additional CPUs, etc).

Target Driver Filter. The operation of the target driver filter 160 isdescribed with respect to the processing of a type of block commandpacket, known as an iSCSI encapsulation packet 180 (sometimes referredto as “command packet”) that includes a SCSI command, to generate an IOB182. To elaborate, the command packet 180 is a packet that encapsulatesa SCSI block command and other information, is received at one of theEthernet cards 44A-44D, and processed by the Ethernet hardware driver108, TCP/IP protocol processor 110, and iSCSI protocol processor 140prior to being provided to the target driver filter 160. It should beappreciated that the target driver filter 160 can be adapted to operatewith block commands other than SCSI block commands, networks other thanthe Ethernet, and network protocols other than TCP/IP.

The IOB 182 is a data structure that stores data/metadata associatedwith the processing of the SCSI block command. More specifically, theIOB 182 provides multiple fields for holding data/metadata relating tothe processing of the SCSI block command. The target driver filter 160builds the IOB 182 and populates certain fields of the IOB withdata/metadata from the command packet 180. The IOB 182 is then providedto each of the other filters in the filter stack 132 that is involved inthe executing or attempting to execute the SCSI command (e.g., goingdown the stack). Each of these other filters can, if needed, readdata/metadata from one or more fields in the IOB 182 and, if needed,write data/metadata to one or more fields in the IOB 182. After the SCSIcommand is executed (e.g., data is written to or read from a data store)or fails to execute, the IOB 182 is then provided to each of the filtersin the filter stack 132 that is involved in providing the result of theof the processing of the SCSI command (e.g., going up the stack).Ultimately, the IOB 182 is provided to the target driver filter 160which uses the IOB 182 to create an iSCSI encapsulation packet thatincludes the result of the processing of the SCSI command, e.g., aresult packet. The result packet is then provided to the networkprocessors 130 for additional processing and transmission of the resultspacket towards the initiator that originated the command packet.

iSCSI Encapsulation Packet with SCSI Command. The command packet 180 iscomprised of an Ethernet field 184, an IP field 186, a TCP field 188,and an iSCSI field 190. The iSCSI field 190 is, in turn, comprised of abasic header segment 192, an additional header segment 194, a headerdigest 196, a data segment 198, and a data digest 200. The basic headersegment is comprised of an Opcode field 202, a DataSegLen field 204, aLUN field 206, and a SCSI command data block 208. The data digest 200includes a data cyclic-redundancy-check (CRC) field 210.

IOB. The IOB 182 is comprised of an Initiator ID field 220, a VolIDfield 222, a PageMode field 224, an LBA/PageNum field 226, aSectorCount/PageOffset field 228, a Command field 230, an ErrorCode 232field, an ErrorOffset field 234, a NumberOfDataSegments field 236,DataSegmentVector field 238, a DataCRCVector field 240, a Layerld field242, a QoS attributes field 244, a StoreID field 246, a StoreLBA field248, an In Time Stamp field 250, an Issuer stack field 252, and anXtraContext field 254. The QoS attributes field 244 is comprised of acriticality field 260A, AllowedStores field 260B, AllowedLatency 260C,ProjectedImpact 260D, and ImpactArray 260E. The Impact Array 260Eincludes impacts for each of the physical components of the primary datastorage system (e.g., CPU, memory, SAS, SSD, and Ethernet) and thesoftware components (e.g., volume, criticality, and initiator). Itshould be appreciated that the AllowedLatency 260C and the InTimeStamp250 are used in a “headroom” evaluation (e.g., an evaluation as to theamount of time available to perform an operation) in such a way that asfilters higher in the stack consume time operating on an IOB, thefilters lower in the stack have less “headroom” to operate on the IOB.

After the target driver filter 160 receives the command packet 180, thetarget driver filter 160 builds the IOB 182 and populates certain fieldsof the IOB 182 with values from or derived from the command packet 180.It should be appreciated that a value associated with a field issometimes referred to simply by the field name.

Specifically, the target driver filter 160 uses data/metadata in the TCPfield 188 of the command packet 180 to lookup the value in a TCP sessiontable associated with an earlier login phase for the Initiator ID field220 of the IOB 182.

The target driver filter 160 uses data/metadata in the LUN field 206 ofthe command packet 180 to derive a value for the VolID field 222 of theIOB 182, e.g., the volume within the primary data storage system 28 towhich the SCSI block command relates. The value in the VolID field 220reflects the priority (e.g., mission critical, business critical,non-critical) that the administrator has associated with the data blocksthat are associated with volume.

If the value in the PageMode field 224 is not automatically establishedas “off” when the IOB 182 is first established, the target driver filter160 sets the value of the PageMode field 224 to “off” to indicate thatthe IOB 182 initially relates to a block or blocks of data within avolume and not to a block or blocks of data within a page, a larger unitof memory than a block. Moreover, the “off” value in the PageMode field224 also indicates that the values established or to be established inthe LBA/PageNum field 226 and SectorCount/PageOffset field 228 are LBAand SectorCount values and not PageNum and PageOffset values.

The target driver filter 160 uses data/metadata in the SCSI Command DataBlock field 208 to populate the command field 230 with the SCSI command(e.g., a block read command or a block write command), the LBA/PageNumfield 226 with the address of the first logical block address within thevolume to which the SCSI command relates, and the SectorCount/PageOffsetfield 228 with the number of sectors (or blocks) beginning at thespecified LBA to which the SCSI command relates. Sometimes a block readcommand is referred to as a read block command. Similarly, sometimes ablock write command is referred to as a write block command.

If the values of the ErrorCode field 232 and ErrorOffset field 234 arenot automatically set to “null” or irrelevant values when the IOB 182 isfirst established, the target driver filter 160 establishes such valuesin these fields. The ErrorCode field 232 holds an error code value thatis subsequently established by a filter in the filter stack 132 andindicative of a type of error encountered in the processing of the SCSIcommand or in the returning of the result of the processing of the SCSIcommand. The ErrorOffset 234 field holds an offset value that furtherdefines the type of error identified in the ErrorCode field 232.

If the SCSI command is a write command, the target driver filter 160uses the data segment field 198 to establish values in theNumberOfDataSegments field 236 and the DataSegmentVector field 238. Toelaborate, in the case of a write command, the target driver filter 160places the data (sometimes referred to as “write data”) in the DataSegment field 198 into memory (e.g., memory store 52A or 52B). Inplacing the data in the Data Segment field 198 into memory, the datafrom the Data Segment field 198 may be broken into two or morenon-contiguous segments. The target driver filter 160 places the numberof data segments that are established in memory in theNumberOfDataSegments field 236 and the address and length of each of thesegments established in memory in the DataSegmentVector field 238. Ifthere is more than one segment established in memory, the target driverfilter 160 calculates a cyclic redundancy check (CRC) or possiblyanother form of hash for each of the segments and places each of the CRCvalues in the DataCRCVector field 240. If there is only one segmentestablished in memory (e.g., all of the data in the Data Segment field198 was copied into a single segment in memory), the target driverfilter 160 copies the value that is in the Data CRC field 210 to theDataCRCVector field 240. It should be appreciated that a dataverification techniques other that CRC can be employed in place of CRC.

After the DataCRCVector field 240 has been populated, the target driverfilter 160 calculates a CRC on the data in the Data Segment 198 andcompares the calculated CRC to the CRC value (if present) in the DataCRC field 210. If there is a difference between the calculated CRC andthe CRC in the field 210, then the data in the Data Segment 198 hassomehow been corrupted. In this case, the processing of the SCSI commandis aborted and the target driver filter 160 prepares a result packetindicating that the command failed to execute. The result packet ispassed on to the network processors 130 for processing and transmissionto the initiator.

If the SCSI command is a read command, the target driver filter 160populates the NumberOfDataSegments field 236, the DataSegmentVectorfield 238, and the DataCRCVector fields with “null” or irrelevantvalues. When a filter that is capable of satisfying the read, the filterwill place the data (sometimes referred to as “read data”) into memory(e.g., memory store 52A or 52B) and populates the NumberOfDataSegmentsfield 236 and the DataSegmentVector field 238 with the count and addressof the read data blocks in memory.

If the values of the LayerID field 242, QoS Attributes field 244,StoreID field 246, StoreLBA field 248, IssuerStack field 252, andXtraContextStack field 254 are not automatically set to “null” orirrelevant values when the IOB 182 is first established, the targetdriver filter 160 establishes such values in these fields.

The target driver filter 160 places an “In” time in In Time Stamp field250 that reflects the point in time when or about when the target driverfilter 160 passes the IOB 182 to the next filter in the filter stack132.

The IssuerStack field 252 is used by a filter in the filter stack 132that is operating on a command IOB (e.g., when the flow of the IOB isdown the filter stack 132) to indicate that the filter needs to doadditional processing when the result IOB is propagating up the stack(e.g., when a result of the execution of the SCSI command or failure toexecute the SCSI is being prepared). The XtraContextStack field 254 is afield that a filter can use to store additional context information whenthe filter has indicated in the IssuerStack field 252 that the filterneeds to do additional processing when the IOB is propagating up thestack. Because several filters can indicate a need to do additionalprocessing when a result IOB is propagating up the stack, theIssuerStack field 252 has a stack structure in which each filter thatneeds to do additional processing “pushes” down an indication of theneed to do additional processing onto the “stack.” As a result IOBpropagates up the stack, a filter that “pushed” down an indication of aneed to do additional processing “pops” off or removes the indicationfrom the IssuerStack field 252 after the additional processing of theIOB is completed by the filter. The XtraContext Stack field 254 also hasa push/pop structure that functions in a substantially similar way tothe IssuerStack field 252.

Once the building of the IOB 182 is complete and no errors wereencountered in the building of the IOB 182 that caused the processing ofthe SCSI command to be aborted, the target driver filter 160 (a)communicates with the statistics database 168 so as to cause a “pendingIOB” statistic to be incremented, (b) populates the IssuerStack field252 and XtraContextStack 254 fields as needed.

Later, when a result IOB 182 is propagating up the filter stack 132 andreaches the target driver filter 160, the current time is obtained, the“In” time stored in the In Time Stamp field 250 is obtained, and thetotal latency associated with the processing of the IOB is calculated,e.g., the elapsed time between when the “In” time value was obtained bythe target driver filter 160 and the when the current time was obtained.The target driver filter 160 updates initiator and volume tables in thestatistics database 168 with the total latency value. It should beappreciated that other tables or statistics in the statistics database168 may also be updated. Additionally, the target driver 160 builds theresult packet and provides the result packet to the network processors130 for further processing and communication to the initiator.

Foreground Filters

The foreground filters 162 include an I/O forward filter 270, a layermap filter 272, a quality-of-service (QoS) filter 274, statisticscollection filter 276, a pattern deduplication filter 278, a dictionaryde-duplication filter 280, and an I/O journal filter 282.

I/O Forward Filter. An initiator can send a command packet to theprimary data storage system 28 that relates to a volume for which thestorage processor that initially starts processing the IOB relating tothe command packet is not responsible. The I/O forward filter 270operates to identify this situation and forward the IOB to the storageprocessor that is responsible for the volume.

By way of background, when an administrator computer 34 communicateswith one of the storage processors 46A, 46B via the management stack 100to request the creation of a volume, the filter manager 166 associatedwith the storage processor creates the volume and updates a volumeownership table to indicate that the particular storage processor and noother storage processor in the primary data storage system 28 isresponsible for the volume. With reference to FIG. 4, an example of avolume ownership table 286 is illustrated. Additionally, the filtermanager 166 indicates to the fail-over manager 104 that the volumeownership table has changed. In response, the fail-over manager 104communicates that there has been a change in the volume ownership tableto the fail-over manager associated with each of the other storageprocessors in the primary data storage system 28. There are a number ofother situations that cause a change in the volume ownership table andthe change to be communicated to the other fail-over managers. Forinstance, the destruction of a volume causes such a change in a volumeownership table. Another situation that causes a change in the volumeownership table is a fail-over, e.g., a situation in which the storageprocessor that is responsible for a volume cannot adequately service thevolume and responsibility for the volume is transferred to anotherstorage processor. In any event, the volume ownership table identifiesthe volume(s) for which each storage processor in the primary datastorage system 28 is responsible.

The I/O forward filter 270 obtains the volume id to which the SCSIcommand relates from the VolID field 222 of the command IOB and uses thevolume id to determine, using the volume ownership table, if the “home”storage processor (e.g., the storage processor that is executing the I/Oforward filter) is the storage processor that is responsible for theidentified volume. If the volume is a volume for which the “home”storage processor is responsible, the IOB is passed on to the layer mapfilter 272. If, however, the volume is not a volume for which the “home”storage processor is responsible, the I/O forward filter 270 forwardsthe IOB to the I/O forward filter associated with the “foreign” storageprocessor that the volume ownership table indicates is the “owner”storage processor of the volume. In the illustrated embodiment, theforwarding of the IOB involves the use of the switches 50A, 50B. When aresult IOB subsequently reaches the I/O forward filter of theforeign/owner storage processor, the result IOB is forwarded back to theI/O forward filter 270 of the “home” storage processor. The “home”storage processor passes the result back up the stack so that the resultcan be placed in a result packet and sent to the originating initiator.

Layer Map Filter. By way of background, the primary data storage system28 provides the ability to take a “snapshot” or “clone” of a volume at aparticular point in time. The snapshot function is implemented usinglayers or versions. The top layer of a layer stack may be read-write andassociated with a particular volume (e.g., a clone). Lower layers in alayer stack may be read only and can be associated with multiple volumes(e.g., a snapshot or snapshot version). A particular volume can haveseveral layers or versions of snapshots, each created at a differentpoint in time. Each layer or version, other than the original or “0”layer, may have a pointer that links the layer or version to the nextmost recently created layer or version for the volume. Each layer orversion, other than the “0” layer, may identify the blocks in the volumethat have been written since the creation of the prior layer or versionof a snapshot. When a snapshot command is executed with respect to avolume, a new layer (e.g., a new snapshot, a new version of a snapshot)is created for the volume, the new layer is assigned a unique layer id,a volume information table is updated so that the layer id of the newlayer is associated with a volume, and a logical block address offsetthat is specified by an administrator is also associated with thevolume. The blocks identified in the new layer or version of thesnapshot can be both written and read until such time as an even newerlayer is created. As such, the new layer is considered a read/writelayer. Relatedly, the creation of the new layer prevents the blocksidentified in the prior layer from being written. As such, the priorlayer is considered a read-only layer. Because the execution of thesnapshot command creates a new layer that is a read/write layer andcauses the prior layer to transition from a read/write layer to aread-only layer, the prior layer is the snapshot of the volume orversion of the snapshot of the volume at the time of the creation of thenew layer.

FIG. 5 is an example of a layer map 290 and an associated volumeinformation table 292. The layer map 290 identifies volumes A, B, C withvolume A associated with one initiator and volumes B and C associatedwith another initiator. Further, layers 1, 2, and 3 have beenestablished with respect to volume A, with layer 3 being the newestlayer relating to volume A. Layers 4 and 1 have been established withrespect to volume B. Layer 5 has been established with respect to volumeC. Layer 5 essentially represents the creation of volume C. The creationof layer 3 caused the volume information table 292 to be updated toreflect that the newest layer associated with volume A is layer 3.Further, the snapshot command that caused the creation of layer 3specified an LBA offset of zero, which is also reflected in the volumeinformation table 292. Lastly, the creation of layer 3 in response tothe snapshot command also created a snapshot of volume A that isreflected in layers 0, 1, 2 as of the time layer 3 was created. Thecreation of layer 4 caused the volume information table 292 to beupdated to show layer 4 as being the newest layer associated with volumeB and to reflect a specified LBA offset of zero. The creation of layer 4also created a snapshot of volume B that is reflected in layers 1 and 0,with layer 1 being shared with volume A. The creation of layer 5 causedthe volume information table 292 to be updated to indicate that layer 5is the newest layer associated with volume C and to show a specified LBAoffset of zero.

The layer map filter 272 receives the IOB provided by the I/O forwardfilter 270 and processes the IOB to determine a layer id (LID) and alayer logical block address (LLBA) for the related SCSI command. Morespecifically, the layer map filter 272 uses the volume id specified inthe VolID field 222 to index into the current volume information table292 to determine the newest LID associated with the volume and LBAoffset associated with the volume. The layer map filter 272 populatesthe LayerID field 242 with the LID retrieved from the volume informationtable. If the offset retrieved from the volume information table isnon-zero, the layer map filter 272 revises the LBA in the LBA/PageNumfield 226 to reflect the LLBA, which is the current LBA value plus/minusthe retrieved offset value. The layer map filter 272 uses the LID andLBA to index into a layer-store table (e.g., FIG. 8) and retrieve theStoreID and StoreLBA values to populate the StoreId field 246 andStoreLBA field 248 of the IOB.

It should be appreciated that certain of the fields in the IOB provide amechanism for storing values that allow IOB s to be processed out oftime sequence to realize certain benefits but still give the same endresult that would occur if the commands were executed in time sequence.The benefit(s) that can be realized by processing IOBs out of timesequence vary. For example, reordering a group of IOBs can be done inthe IO Journal filter 282 to realize data space and/or time-speedbenefits relative to a data store to which data is being moved orcopied. In contrast, reordering of a group of IOBs can be done in theQuality of Service filter 274 to implement the desired quality ofservice for the various initiator(s) utilizing the primary data storagesystem. Even though there are or may be benefits associated withprocessing IOBs out of time sequence, it is desirable and perhapsnecessary to get the same result for each IOB processed out of timesequence order as would be obtained if the IOBs were processed in timesequence order. For example, if a group of IOBs had a read IOB later intime than a write IOB to the same layer and LBA and these IOBs wereexecuted such that the read IOB occurred before the write IOB, adifferent result would be obtained than if the IOBs were executed intime sequence order. However, the fields in the IOB provide a mechanismfor getting the same result as if the IOBs were executed in timesequence order.

In the illustrated embodiment, the fields of the IOB that provide themechanism for executing IOBs out of time sequence order and yetobtaining results upon the execution of the IOBs as if executed in timesequence order include the InTimeStamp 250, LayerID field 242, StoreIDfield 246, StoreLBA field 248 of the IOB. An example that demonstrateshow this mechanism operates involves an IOB relating to a snapshotcommand and two IOBs each relating to a write block command. In thisexample, it is only necessary to use the value in the LayerID field 242to achieve the same result in executing each of the IOBs out of theiroriginal order as would be obtained if the original order was retained.In the example, the original time sequence of IOBs extending from firstreceived IOB to last received IOB is:

(ai) Write Block to Volume A, LBA=11 LayerID=null;

(bi) Create Snapshot, LayerID=3 as a child of LayerID=2 (see FIG. 5);and

(ci) Write Block to Volume A, LBA=12 LayerID=null.

If this sequence were processed by the Layer Map filter 272 and the timesequence order was maintained, the Layer Map filter 272 would update theLayerID fields and the sequence of IOBs would appear as follows:

(ao) Write Block to Volume A, LBA=11 LayerID=2;

(bo) Create Snapshot, LayerID=3 as a child of LayerID=2 (see FIG. 5);and

(co) Write Block to Volume A, LBA=12 LayerID=3.

If the time sequence order of these IOBs is altered by the Layer Mapfilter 272 to realize a “backup of data” benefit associated with theexecution of a snapshot command as soon as reasonably possible afterrecognizing the presence of a snapshot command in a group of IOBs, theLayer Map filter 272 would reorder the sequence of IOBs and updates theLayerID fields in the IOBs as follows:

(aor) Create Snapshot, LayerID=3 as a child of LayerID=2 (see FIG. 5);

(bor) Write Block to Volume A, LBA=12, LayerID=3; and

(cor) Write Block to Volume A, LBA=11; LayerID=2.

A comparison of the (ao)-(co) sequence to the (aor)-(cor) sequencereveals that execution of the commands in either sequence produces thesame results. It should be appreciated that the foregoing is arelatively simple example that only required the use of the Layer IDfield to achieve the same results as if the IOBs were executed in theoriginal sequence. Different IOB sequences may need to make use ofanother one of the

InTimeStamp 250, LayerID field 242, StoreID field 246, StoreLBA field248, or a combination of two or more of these fields, or some otherfield that needs to be defined to handle a particular sequence ofcommands that cannot be adequately addressed by a combination of thenoted fields. Further, it should be appreciated that the use of thenoted fields and/or other fields in the IOB can be used in other filtersto reorder IOBs as received by the filter to obtain some benefit but yetachieve the same results as if the IOBs were executed in the orderreceived. For example, filters that implement this functionality includethe Quality of Service filter 274 and IO Journal filter 282.

Quality of Service (QoS) Filter. The quality-of-service (QoS) filter 274generally provides predictable data storage performance to one or moreinitiators that utilize a shared data storage system (e.g., the primarydata storage system) with multiple volumes. The desired performance of aparticular volume (criticality) is established by the administratorusing the administrator computer 34 to communicate with the managementstack 100. When the administrator uses the administrator computer 34 tocreate a volume, the administrator also uses the administrator computer34 to associate a criticality with the volume. The management stack 100maintains a table/tables that identifies each of the initiators that theprimary data storage system 28 will service and the criticalityassociated with each of the volumes that have been created. The“criticality” associated with a volume is reflected in certainperformance or quality of service goals. As such, a volume that has“highly critical” criticality necessarily has relatively highperformance goals. A volume with “non-critical” criticality hasrelatively lower performance goals. The group of attributes that is usedto reflect performance goals of the primary data storage system 28 withrespect to a volume includes, allowed stores, latency, throughput, andinput/out operations per second (IOPS). An allowed store is a store thata volume is allowed to use during the processing, storing, or retrievingof data for a command packet/IOB. Latency is a measure of the elapsedtime between when the filter stack 132 begins the processing of commandpacket/IOB and when the filter stack 132 finishes preparing a replypacket/IOB. Throughput is a measure of the number of bytes prepared fortransfer (read/write) per unit of time within the filter stack 132 withrespect to a volume. IOPS is a measure of the number of IOBs processedwithin the filter stack 132 per unit of time with respect to a volume.The specification of a criticality for a volume is embodied in a goalwith respect to each of these attributes. It should be appreciated thata greater number, lesser number, and/or different attributes may beappropriate in certain situations. It should also be appreciated thattwo volumes with the same criticality can have the same or differentquality of service or performance goals.

It should be appreciated that the performance of a data store in theprimary data storage system 28 can also be characterized in terms oflatency, throughput, and IOPS. Further, this “store performance” of adata store is or may be relevant to whether the performance goals withrespect to a volume are being met. As such, the production of statisticsrelating to the “store performance” of data stores in the primary datastorage system 28 are produced and available for use in assessingperformance with respect to a volume. Further, other hardware andsoftware in the primary data storage system 28 are also be characterizedand monitored for use in assessing performance with respect to a volume.

Generally, the QoS filter 274 operates to sort IOBs that are associatedwith different volumes having different criticalities (e.g., differentperformance goals) so as to try to meet the goals of each volume. Morespecifically, the QoS filter 274 receives an IOB from the layer mapfilter 272 and processes the IOB to perform: (a) a first sort of the IOBaccording to the volume ID, e.g., according to the criticalityassociated with the volume, (b) a second sort of the IOB according tothe projected impact of the processing of the IOB on the data storagesystem at the primary data storage system 28, the projected impacttaking into account certain metrics/statistics relating to the operationof the primary data storage system 28, and (c) a third sort of the IOBinto an IOB execution stack based upon the criticality associated withthe volume identified in the IOB (first sort), the projected impact(second sort), past usage of the primary data storage system 28 asreflected in certain metrics/statistics, the current state of theprimary data storage system 28 including the state of each of thestores, each of the switches, each of the storage processors, and eachof the network cards (e.g., Ethernet, FC, or other network cards) asreflected in certain metrics/statistics.

FIG. 6 is an example of the operation of the QoS filter 274 with respectto three volumes, each with a different criticality. The first volumehas a “mission critical” criticality; the second volume has a “businesscritical” criticality that is less than “mission critical” criticality;and a third volume has a “non-critical” criticality that is less than“business critical” criticality. As such, there are differentperformance goals associated with each of the volumes in terms oflatency, throughput, and IOPS. Further, one or more of the initiators38A-38C is sending block command packets to the primary data storagesystem 28 that relate to the three volumes. Each of the block commandpackets being processed to generate an IOB, such as IOB 182.

The QoS filter 274 places each IOB that is received from the layer mapfilter 272 into first-in-first-out input queue 300. The QoS filter 274processes each of the IOBs in the queue 300 in the order that the IOBwas received in the queue 300. The following describes the furtherprocessing of the IOB 182 by the QoS filter 274.

The QoS filter 274 includes a group scheduler 302 that sorts IOBsaccording to the criticality associated with the volume to which an IOBrelates. To elaborate with respect to IOB 182, the group scheduler 302uses the volume id in the VolID field 222 as an index into a volumeinformation table (e.g. volume information table 292) that indicates thecriticality value associated with that volume. The QoS filter 274 placesthe criticality value (e.g., a whole number in the range of 1-3) in theCriticality field 260A of the QoS attributes field 244 of the IOB 182.As such, the IOB 182 now has an indication of the criticality of theSCSI command associated with the IOB. Further, the QoS filter 274 usesthe criticality value to sort the IOB 182 into one of the three goalschedulers 304A-304C. In this example, because there are three possiblecriticality values, there are three goal schedulers 304A-304C. Itshould, however, be appreciated that there can be as few as two possiblecriticality values and more than three possible criticality values.Further, there is a goal scheduler associated with each possiblecriticality value. Similarly, the QoS filter 160 uses the volume idspecified in the VolID field 222 to index into the volume informationtable 292 to populate the QoS attributes, AllowedStores 260B, andAllowedLatency 260C fields with the Allowed Stores, and Allowed Latencyvalues retrieved from the volume information table 292. Consequently,the IOB 182 now has an indication of the stores that may be used toservice the IOB and the amount of time that can be used to service theIOB.

Each of the goal schedulers 304A-304C processes an IOB received from thegroup schedule 302 to assess the IOB as to the projected impact of theexecution of the SCSI command. In this regard, each IOB is assessed asto whether execution of the SCSI command is likely to primarily affectlatency, throughput, or IOPS. The assessment takes into accountmetrics/statistics obtained from the statistics database 168. Thesemetrics/statistics include volume related statistics. For example,statistics relating specifically to the volume with which the IOB isassociated, statistics relating to “criticality,” e.g., statisticsrelating to a number of volumes that have the same “criticality”, andstatistics relating an initiator, e.g., statistics relating to a numberof volumes associated with a specific initiator can be used. Thestatistics can include any number of factors, including throughput,queue depth, latency, and use count for these volume related statistics.However, currently it is believed that at least latency statistics areneeded. Further, these factors can further include read and writerelated versions of each of throughput, queue depth, latency, and usecount. Moreover, these factors can include current and historicalstatistics. Current statistics being those statistics associated withthe shortest period of time (or shortest resolution) and historicalstatistics being statistics associated with a greater period or periodsof time relative to the shortest period of time. See, example of aportion of a statistics database 258. The use of statistics relating to“criticality” and/or historical statistics facilitates theidentification of imbalances and the like in the processing of IOBassociated with volumes having the same criticality. For example, if theprocessing of IOBS associated with one volume has placed another volumewith the same criticality increasingly behind its quality of servicegoals, the statistical data provides a basis for identifying this issueand taking action to bring the lagging volume back towards its qualityof service goals.

The assessment results in the IOB being placed in one of a latencyqueue, throughput queue, and IOPS queue associated with the goalscheduler. With reference to FIG. 6, because there are three goalschedulers 304A-304C, there are three FIFO latency queues 306A-C, threeFIFO throughput queues 308A-308C, and three FIFO IOPS queues 310A-310C.Further, the goal scheduler also stores the result of the assessment inthe IOB ProjectedImpact 260D field of the QoS Attributes 244.Consequently, the IOB 182 now has an indication of the projected impactof the execution of the command associated with the IOB, in addition toan indication of the criticality of the IOB provided by the groupscheduler 302. It should be appreciated that it is also possible tochange the order of the group scheduler and the goal scheduler such thatthe goal scheduler occurs first and the group scheduler occurs second.

With continuing reference to FIG. 6, the QoS filter 274 includes ashared hardware scheduler 312 that assesses the IOBs that are the nextin line to be processed in each of the latency, throughput, and IOPSqueues (the IOBs that are at the “bottom” of each of the queues) todetermine which IOB will be placed in or merged into an FIFO executionqueue 314, e.g., a queue that defines the order in which the IOBsreceived at the input queue 300 are to be executed. The assessment ofeach of the IOBs takes into account the criticality and projected impactof the execution of the command associated with the IOB that is setforth in the QoS attributes field of each IOB and metrics/statisticsobtained from the statistics database 168. These statistics includehardware related statistics. For example, statistics relating the CPU,Ethernet cards, and stores (e.g., SSD) can be employed. These factorscan include throughput, queue depth, latency, use count. Further,current and/or historical versions and/or read and/or write versions ofthese factors can be used. It should be appreciated that the comparisonof the IOBs from the goal scheduler output queues to one another arecomparisons of different volumes that have different criticalities anddifferent quality of service goals (IOPs, throughput, and latency). Forexample, if the next selected IOB is throughput related the sharedhardware scheduler 312 will use information in the statistics database168 to determine a store that has available bandwidth to process thecommand and send the IOB down the stack “tagged” with that store as thedestination.

Once the shared hardware scheduler 312 makes a determination as to thenext IOB that is to be placed in the execution queue 314, the IOB is“popped” off the queue with which it is associated and the IOB that wasbehind the “popped” IOB takes the place of the “popped” IOB of thequeue. The shared hardware scheduler 312 makes its next assessment withrespect to the “new” IOB on the queue from which the IOB was “popped”and the “old” IOBs that were associated with the other queues. Forexample, with respect to FIG. 6, at a given point in time, each of IOBs316A-316I is the next in line to be “popped” from their respectivequeues. The shared hardware scheduler 312 evaluates each of these IOBsto determine which one of IOBs 316A-316I is the next to be placed in theexecution queue 314. If, for example, the shared hardware controller 312decided that IOB 316A was the next to be placed in the execution queue314, the next evaluation by the shared hardware controller 312 would bewith respect to IOBs 316B-316I and IOB 316J, which has taken the placeof IOB 316A at the head of the IOPS queue 310A. Before an IOB is placedin the execution queue 314, the related IOB is updated so as to “push”an indication onto the IssuerStack field 252 that the QoS filter 274needs to do additional processing on the IOB when the IOB is propagatingup the filter stack 132.

It should be appreciated that FIG. 6 shows a specific implementation ofthe QoS filter 274. The QoS filter 274 is more generally characterizedas producing a sum of weighted factor values for an IOB that indicate orsignify the rank of the IOB relative to other IOBS being processed. Inthis regard, the factors can include the volume and hardware relatedthroughput, queue depth, latency, use count, the notedcurrent-historical-read-write versions thereof. The values for thesefactors are obtained from the IOB and the statistics database. Theweighted coefficients associated with each factor being dynamicallyadjustable to reflect the changing priorities with respect to thevolumes and hardware due to what is typically a changing workload beingplaced on the system.

Later, when the IOB 182 is propagating up the filter stack 132 andreaches the QoS filter 274, the QoS filter 274, informs the sharedhardware scheduler 312 that the queues should be re-evaluated.

Statistics Filter. Generally, the statistics filter 276 operates tocollect certain initiator and volume related data/statisticalinformation for each IOB passed to the statistics filter 276 from theQoS filter 274 when the IOB is going down the filter stack 132. Toelaborate with respect to IOB 182, the statistics filter 276 processesthe IOB 182 to obtain the initiator id from the InitiatorID field 220,the volume id from the VolID field 222, the sector count from theSectorCount/PageOffset field 228, and the “In” time stamp value from theIn Time Stamp field 250. The statistics filter 276 also obtains thecurrent time from the operating system. The statistics filter 276 usesthe value of the “In” Time Stamp and the current time to calculate thelatency that the IOB has experienced between when the “In” Time Stampvalue was established in the target driver filter 160 and when thecurrent time is obtained by the statistics filter 276 (hereinafterreferred to as “first latency”). The statistics filter 276 communicateswith the statistics database 168 so as to: (a) update a table for theinitiator that is maintained in the database to reflect that an IOBassociated with the initiator will be processed that has the sector sizeobtained from the IOB and that the IOB has experienced the calculatedfirst latency and (b) update a table for the volume that is maintainedin the database to reflect that an IOB associated with the volume willbe processed that has the sector size obtained from the IOB and that theIOB has experienced the calculated first latency.

The statistic filter 276 also pushes an indication onto the IssuerStackfield 252 of the IOB 182 that the statistics filter 276 needs to doadditional processing when the IOB is propagating up the filter stack132. Further, the statistic filter 276 also pushes the current time ontothe XtraContextStack field 254.

Later, when the IOB 182 is propagating up the filter stack 132 andreaches the statistics filter 276, the statistics filter 276 obtains thetime from the XtraContextStack field 254 (which is no longer the currenttime), obtains the “new” current time, and calculates a second latency,e.g., the elapsed time between when the time value was obtained that waspushed onto the XtraContextStack field 254 and the IOB was propagatingdown the filter stack 132 and the when the “new” current time wasobtained. The statistics filter 276 updates the initiator and volumetables in the statistics database 168 with the second latency value.Further, the statistics filter 276 uses the values from the ImpactArray260E to update the statistics database 168. When updating the databaseit may be necessary to update multiple rows of data, (e.g. when updatingthe CPU statistics it may be required to update the row for Second,Minute, Hour, and Day).

Pattern De-Duplication Filter. Generally, the pattern de-duplicationfilter 278 operates to preserve storage capacity and reduce turnaroundtime to the initiator at the primary data storage system 28 bypreventing a block(s) of identical data that are frequently written tothe primary data storage system 28 from being written multiple timeswith each such writing of the block(s) of data consuming additionalstorage capacity and time. More specifically, the pattern de-duplicationfilter 278 operates to identify a block(s) of data that have a patternwhich can be readily calculated. Characteristic of a pattern is that thevalues of each byte of data in a block can be calculated. For example,if the values of the bytes of data in a block represent a triangle wavewith known characteristics (period, amplitude, phase, sampling frequencyetc.), the value of each of the bytes in the block is susceptible tocalculation. A pattern that can be “readily” calculated is a patternthat can be calculated or retrieved and the IOB completely processed(e.g., a result packet is prepared) within the latency associated withthe volume. It should be appreciated that, for a given latency, thenumber of patterns that can be readily calculated increases withincreasing processing speed.

Initially, with respect to an IOB associated with a SCSI write-relatedcommand, the pattern de-duplication filter 278 makes a “headroom”calculation to determine if there is sufficient time available toperform the operations associated with pattern deduplication, whichincludes the time needed to identify a calculation engine that may beable to calculate a pattern associated with the write data and the timeneeded to determine if there is a match between the write data and thedata produced by the selected calculation engine. In this regard, thereneeds to be sufficient time to conduct these operations within whatevertime remains in the allowed latency 260C.

Generally, the pattern de-duplication filter 278 assesses data in thefirst block of data associated with each IOB having a SCSI write-relatedcommand to determine if a known calculable pattern of data is present.If all of the data in the first data block has a known calculablepattern, the pattern de-duplication filter 278 proceeds to assess thesecond and any additional blocks of data associated with the IOB. If allof the data in all of the blocks of data associated with the IOB have aknown calculable pattern, there are two possibilities.

First, if the current values in the StoreID field 246 and the StoreLBAfield 248 of the IOB are not currently identified as being the values ofthe StoreID and the StoreLBA associated with the pattern, the currentvalues in the StoreID field 246 and StoreLBA field 248 in the IOB areupdated. The current values in the StoreID and StoreLBA fields wereestablished in the layer map filter 272. A portion of the applicationmemory that is dedicated to storing a particular pattern calculator isidentified as a calculation engine 320. Although only one calculationengine 320 is shown in FIG. 2, there is a calculation engine for eachpattern calculator. Because the current values in the StoreID field 246and the StoreLBA field 248 do not point to the calculation engine 320,the values in the StoreID field 246 and the StoreLBA field 248 need tobe updated to point to the calculation engine. Once the values forStoreID field 246 and StoreLBA field 248 have been updated, the patterndeduplication filter 278 updates the command field 230 of the IOB so asto reflect that a de-dup write needs to be done and passes the IOB downthe filter stack 132.

Second, if the current values in the StoreID field 246 and the StoreLBAfield 248 of the IOB are currently identified as being the values of theStoreID and the StoreLBA associated with the pattern, the values in theStoreID field 246 and StoreLBA field 248 in the current IOB are notmodified. The values in the StoreID and StoreLBA fields were establishedin the layer map filter 272 and respectively point to the relevantcalculation engine for calculating the pattern. Because the pattern ofthe blocks of data has not changed from the prior IOB with the samevalues in the VolId field 222 and the LBA/PageNum field 226, the patternde-duplication filter 278 places a “success” code in the error codefield 232 and causes the IOB to start propagating up the filter stack132, thereby indicating that the SCSI write command of the IOB has beencompleted.

If the data in any block(s) of data associated with the IOB do not havea known calculable pattern, the pattern de-duplication filter 278determines the pattern deduplication is not possible and passes the IOBon to the dictionary de-duplication filter 280.

While the assessment of the first block of data associated with the IOBcould be done with respect to each known calculable pattern, the patternde-duplication filter 278 avoids doing so by making an initialcomparison of two bytes in a block of data and using the result of thecomparison for concluding that the data in the block: (a) potentiallyhas one of the known calculable patterns or (b) does not possess one ofthe known calculable patterns. This two byte comparison is a form of a“hash” calculation. It should be appreciated that methods other than thenoted two byte comparison (a form of hash) can be applied (e.g. CRC orhash) as long as the methods can make the determination within thelatency constraint, e.g., the allowed latency set forth in volumeinformation table 292. If the comparison indicates that the data in theblock potentially has one of the known calculable patterns, the patterndeduplication filter 278 proceeds to assess the data in the block todetermine whether the data in the block actually does have theidentified, known calculable pattern.

More specifically, the pattern de-duplication filter 278 utilizes thepattern calculator to calculate the value that a byte(s) of the patternshould have if present in the data block and compare each such value tothe actual value associated with the byte(s) in the data block.Generally, it is desirable to utilize a calculator that is efficient,e.g., makes a determination of whether or not the pattern is present inthe data more quickly rather than less quickly so as to make thedetermination within the latency constraint, e.g., the allowed latencyset forth in volume information table 292. Further, the comparison isdone in the fastest data store available, typically memory store 52A and52B.

For example, if the pattern is a triangle wave and there is an evennumber of cycles of the triangle wave in a block of data, a relativelyefficient calculator for determining if this wave pattern is present ina block would: (a) with respect to the potential first cycle of the wavepattern in the block, use the pattern calculator to calculate a firstvalue for the wave pattern and compare that value to the two bytes inthe data that should have the calculated value if a first cycle of thetriangle wave is present in the block and (b) repeat this calculationand comparison to the values associated with different bytes in the datablock until the presence of the first cycle of a triangle wave in thedata is either confirmed or disaffirmed. If a first cycle of thetriangle wave is not present, the pattern de-duplication filter 278passes the IOB on to the dictionary de-duplication filter 280. If thepresence of a first cycle of the triangle wave in the data is confirmed,the calculator proceeds to compare the data associated with the firstcycle of the triangle wave to the data in the block that might be thesecond cycle of the triangle wave to either confirm or disaffirm thepresence of the second cycle of the triangle wave. If the second cycleof the triangle wave is not present, the pattern deduplication filter278 passes the IOB on to the dictionary de-duplication filter 280. Ifthe presence of the second cycle of the triangle wave is confirmed, thecalculator proceeds to compare the data associated with the first andsecond cycles of the triangle wave to the data in the block that mightbe the third and fourth cycles of the triangle wave. This process ofcomparing groups of bytes that increase in number by a factor of twowith each comparison continues until either the presence of the patternin all of the blocks associated with IOB is confirmed or disaffirmed.

Read De-Duplication Operation. Generally, the pattern de-duplicationfilter 278 operates on an IOB having a SCSI read-related command todetermine if the data at the identified volume id and LBA is data thathas been previously de-duplicated in the processing of an IOB with aSCSI write-related command. More specifically, the patternde-duplication filter 278 obtains the value in the StoreID field 246. Ifthe value in the StoreID matches a StoreID assigned to a calculatorengine (e.g., engine 320), the pattern de-duplication filter 278concludes that the read-related command in the IOB relates to patterndata that has been de-duplicated. Further, the de-duplication filter 278obtains the value in the StoreLBA field 248 to identify the vector intothe calculator for calculating the particular pattern and uses thecalculator to create the block(s) of patterned data in the memory store(e.g., CPU bus memory 52A or CPU bus memory 52B), if the block(s) ofpatterned data do not already exist in the memory store. The patternde-duplication filter 278 then updates the value in theDataSegmentVector field to point to the address in the memory store(e.g., CPU bus memory 52A or 52B) that has the copy of the calculatedpattern. Further, the pattern de-duplication filter 278 places a“success” code in the error field 232 and causes the IOB to startpropagating up the filter stack 132, thereby indicating that the SCSIread-related command of the IOB has been completed. If the value in theStoreID does not match a StoreID assigned to a calculator engine, theIOB is passed down the filter stack 132 for further processing.

Dictionary De-Duplication Filter. Generally, the dictionaryde-duplication filter 280 operates to preserve storage capacity andreduce turnaround time to the initiator at the primary data storagesystem 28 by preventing blocks of data associated with an IOB thatconstitute a page (a predefined number of contiguous blocks of data)that are commonly written to the primary data storage system 28 and donot have a readily calculable pattern from being written multiple timessuch that each writing of the page consumes additional storage capacityand time.

By way of background, the dictionary de-duplication filter 280 hasaccess to a dictionary table that is capable of holding a limited andpredetermined number of entries. Each non-null entry in the dictionarytable relates to a page of data identified by an advanced de-duplicationfilter, one of the background filters 164, as being one of the mostcommon pages of data being written to storage. More specifically, eachnon-null entry in the dictionary table for a “dictionary” page hasStoreID and StoreLBA values for a copy of a “dictionary” page that is ona dictionary store 322. Because the dictionary de-duplication filter 280is one of the group of foreground filters and speed of execution is apriority in the foreground, the dictionary store 322 that holds the copyof the “dictionary” page is typically a high-speed store, like memorystore 52A or memory store 52B. The entry in the dictionary table alsoidentifies a portion of data in the relevant “dictionary” page (e.g.,the second 64 bytes of data in the page) that is unique relative to allof the other non-null entries in the dictionary table. While it isfeasible to use different identifying portions of a “dictionary” pagefor each entry (e.g., one entry has the first 64-bytes of a first“dictionary” page and another entry has the second 64-bytes of a second“dictionary” page) as long as the data in each of the portions isunique, the use of the same identifying portion of data from each of the“dictionary” pages facilitates the assessment of whether the pageassociated with an IOB can be de-duplicated. This is a form of hash,other forms of hash are also feasible. Consequently, each non-null entryin the dictionary table relates to the same identifying portion of a“dictionary” page (e.g., the second 64-bytes) as the other entries inthe dictionary table. Further, the data in the identifying portionrelating to a single “dictionary” page is unique relative to all theother non-null entries in the dictionary table. Because the mostcommonly written pages can change over time and the dictionary table hasa limited and predetermined number of entries, the advancedde-duplication filter can change the entries in the dictionary table. Inthis regard, a change to the table may require that a differentidentifying portion of the pages to which the entries in the tablerelate be used to preserve the uniqueness of each entry in the table.The identifying portion of each of the dictionary pages that is uniqueis maintained by the advanced de-duplication filter and available to thedictionary de-duplication filter 280. The advanced de-duplication filteralso ensures that a copy of each of the common pages that is identifiedin dictionary table is in the dictionary store 322.

Initially, with respect to an IOB associated with a SCSI write-relatedcommand, the dictionary de-duplication filter 280 makes a “headroom”calculation to determine if there is sufficient time available toperform the operations associated with dictionary deduplication, whichincludes the time needed to identify a dictionary entry that maycorrespond to the write data and the time needed to determine if thereis a match between the write data and the data in the dictionary entry.In this regard, there needs to be sufficient time to conduct theseoperations within whatever time remains in the allowed latency 260C.

In processing an IOB with a write-related command that relates to ablock(s) of data, the dictionary de-duplication filter 280 determines ifthe write command relates to a page. This determination is made byobtaining the sector count value in the SectorCount/PageOffset field 228in the IOB. If the value is not equal to the number of blocks in a page,the dictionary de-duplication filter 280 passes the IOB on down thefilter stack 132. If, however, the value is equal to the number ofblocks in a page, the dictionary de-duplication filter 280 obtains thesame portion of the page associated with the IOB that is associated withthe identifying portion in each entry in the dictionary table andcompares this portion of the page to each identifying portion in thedictionary table. If there is no match (e.g., the IOB relates to a pagethat is not common enough to justify an entry in the dictionary table),the dictionary de-duplication filter 280 passes the IOB on down thefilter stack 132. If there is a match, then there is a possibility thatthe page associated with the IOB is a match with the “dictionary” pageto which the entry in the dictionary table relates. To determine whetherthere is such a match, the dictionary de-duplication filter 280 comparesthe page associated with the IOB to the copy of the “dictionary” pagethat is located at the StoreID and StoreLBA of the dictionary store 322set forth in the dictionary table. The data associated with the writeIOB and the dictionary page are both in memory store 52A or 52B, thefastest type of store in the illustrated system. As such, the comparisonoccurs more quickly than if the comparison was done in some other storein the system. If there is no match, the dictionary de-duplicationfilter 280 passes the IOB down the filter stack 132. If there is amatch, there are two possibilities.

First, if the current values in the StoreID field 246 and the StoreLBAfield 248 of the IOB are not currently identified as being the values ofthe StoreID and the StoreLBA associated with the copy of the “dictionarypage” in the dictionary store 322, the current values in the StoreIDfield 246 and StoreLBA field 248 in the IOB are updated. The currentvalues in the StoreID and StoreLBA fields were established in the layermap filter 272. Once the values for StoreID field 246 and StoreLBA field248 have been updated, the dictionary de-duplication filter 280 updatesthe command field 230 of the IOB so as to reflect that a dedup writeneeds to be done and passes the IOB down the filter stack 132.

Second, if the current values in the StoreID field 246 and the StoreLBAfield 248 of the IOB are currently identified as being the values of theStoreID and the StoreLBA associated with the copy of the “dictionarypage” in the dictionary store 322, the current values in the StoreIDfield 246 and StoreLBA field 248 in the IOB are not updated. The currentvalues in the StoreID and StoreLBA fields were established in the layermap filter 272. The dictionary de-duplication filter 280 places a“success” code in the error field 232 and causes the IOB to startpropagating up the filter stack 132, thereby indicating that the SCSIwrite command of the IOB has been completed. For example, the primarystorage system 28 has previously persisted the same data at the samelayer and same LBA and therefore does not need to make any changes dueto this IOB.

Read De-Duplication Operation. Generally, the dictionary de-duplicationfilter 280 operates on an IOB having a SCSI read-related command thatneed not relate to a page to determine if the data associated with theidentified volume id and LBA is data that has been previouslyde-duplicated in the processing of an IOB with a SCSI write-relatedcommand relating to the same volume id and LBA. More specifically, thedictionary deduplication filter 280 obtains the value in the StoreIDfield 246 and determines if the value is currently associated with thedictionary store 322. If the value is currently associated with thedictionary store 322, the dictionary de-duplication filter 280 thenupdates the value in the DataSegmentVector field to point to the addressin the memory store (e.g., memory store 52A or 52B) that has the copy ofthe dictionary page and, more specifically, to point the first block ofthe page that has the first block to which the SCSI read commandrelates. Further, the dictionary de-duplication filter 280 places a“success” code in the error field 232 and causes the IOB to startpropagating up the filter stack 132, thereby indicating that the SCSIread-related command of the IOB has been completed. If the value in theStoreID field 246 is not currently associated with the dictionary store322, the IOB is passed down the filter stack 132 for further processing.

I/O Journal Filter. Generally, the I/O journal filter 282 operates withrespect to IOBs in the execution queue 314 that have SCSI write-relatedcommands (de-dup write and write) that have not been fully addressed byan intervening filter to move the actual data that is associated withthe IOBs and currently resident in a non-redundant and/or non-persistentdata store or other information that allows the data to be reproduced toa redundant and persistent data store (e.g., a journal store). Further,because the I/O journal filter is part of the foreground filters 162,the I/O journal filter 282 endeavors to do so in a timely fashion.Because the actual data associated with an IOB or other information thatallows the actual data associated with the IOB to be reproduced is movedto a redundant and persistent data store, the I/O journal filter 282also causes each such IOB to begin propagating up the filter stack 132,thereby acknowledging completion of the write-related command. The I/Ojournal filter 282, in certain embodiments, may therefore acknowledgecompletion of a write command in response to storing data of the writecommand (e.g., the associated IOB) in a journal preserved in anon-volatile storage medium (e.g., SSD 54) of a persistent data store48. In a further embodiment, the I/O journal filter 282 may acknowledgecompletion of a write command before the data has reached its intendeddestination, in a hard disk drive 56, a storage volume, a backup/tapeserver 62, a cloud storage provider 64, or the like, because the data isredundantly and persistently preserved in one or more journals of theone or more data stores 48A, 48B.

There are two characteristics of the I/O journal filter 282 that eachcontribute to the timely processing. The first characteristic is thateach write to the redundant and persistent store is the writing of apage, which may be comprised of a large number of blocks. A page, asused herein, may comprise a fixed-length logical or physical unit,region, or segment of memory or storage. In certain embodiments, a pagemay comprise a smallest unit of data for memory allocation, for transferbetween memory and a data store 48, or the like. As such, for a givennumber of data blocks, the writing of pages requires fewer writesrelative to an approach in which there is a separate write operation foreach block. The second characteristic is that the writes are done tolocations in the redundant and persistent store that haveincreasing/decreasing addresses. For example, a number of page writescould be done to locations 1, 5, 20, and 200 on the store. This avoidsthe time overhead associated with writing to locations that areunordered (e.g., locations 1, 200, 20, and 5).

With reference to FIG. 7, the I/O journal filter 282 in one embodimentoperates on a journal store that is implemented in a redundant fashionbetween the SSDs 54A, 54B, both of which also exhibit persistence. Itshould be appreciated that, while redundant and persistent stores arecommonly utilized, other types of stores that do not exhibit redundancyor persistency can also be employed. Each of the SSDs 54A, 54B, has acopy of a journal 340, a data storage space of known length or capacitythat stores the data associated with the IOBs and related metadata.Redundancy is provided by each of the SSDs 54A, 54B having a copy of thejournal 340. For convenience, the operation of the I/O journal filter282 is described with respect to a single copy of the journal 340, whichmay be referred as the journal 340, with the understanding that changesto one copy of the journal are also made to the other copy of thejournal.

In the illustrated embodiment, the journal 340 has a data storage spaceof 640 Gigabytes. The storage space is divided into a plurality of2-Megabyte journal page (JP) 342. Each journal page 342 has a journalpage header 344 that identifies the journal page within the journal 340.The remainder of a journal page is available to be populated with aplurality of journal entries. A journal entry (JE) 346 is comprised of ajournal entry header (JEH) 348 that stores metadata related to thejournal entry and a journal entry data field 350 capable of storing4-kbytes of actual data associated with an IOB or other information thatallows the actual data associated with the IOB to be reproduced. Thejournal entry data field 350 is further divided into 8 512-byte journalblock 351.

The journal entry header 348 is comprised of a LayerLBA field 420, aLayerID field 422, a StoreID field 424, a StoreLBA field 426, aTimeSeqID field 428, a ValidMask field 430, a Restricted field 432, anda Clean field 434. The JEH fields are populated with the value for thelayer LBA that is present in the LBA/PageNum field 226 of the IOB thatprovided the first 512-byte block in the journal entry data field andthe values in the LayerID, StoreID, and StoreLBA fields of the same IOB.The ValidMask field 430 is also present in the journal entry header 348and is used to identify the 512-byte blocks that are in the journalentry data field 350. For example, if the LBA is 20 and the ValidMaskfield 430 is set to “10001000”, LBAs 20 and 24 are present in thejournal entry data field 350. Initially, the Restricted field 432 is setto a value indicating that the JE is not restricted, e.g., the writeblock operations associated with the JE are not constrained to beingexecuted in the presented sequence. Similarly, the Clean field 434 isinitially set to a value indicating that the JE is “dirty”, e.g., existsonly in the journal 340.

Associated with the journal 340 is a journal table that maps the valuesin the LayerID and LayerLBA fields of the IOB or journal entry header348 to a particular journal page and journal entry. With reference toFIG. 7, an example of a journal table 352 is illustrated.

With the foregoing background in mind, the I/O journal filter 282identifies IOBs in the execution queue 314 that have pending SCSIwrite-related commands (de-dup write and write), e.g., SCSIwrite-related commands that have not been fully addressed by anintervening filter. The I/O journal filter 282 also identifies thecurrently active journal page and journal entry, e.g., the location inthe journal 340 that is to be next in line to be populated withwrite-related data. For example, the currently active journal page couldbe journal page number “20” and the currently active journal entry couldbe journal entry “7”. The currently active journal entry either has nodata in the journal entry data field or there is data in at least thefirst 512-byte journal block and possibly one or more of the immediatelyfollowing 512 byte journal blocks but not in all of the 512-byte journalblocks.

A “working” copy of the currently active journal page is located in theapplication memory of a storage processor. With respect to the “working”copy of the currently active journal page, the I/O journal filter 282further determines if the first 512-byte block of the current journalentry has been written. If this is not the case, the I/O journal filter282 writes the next 512-byte block associated with an IOB into the first512-byte block of the journal entry data field. If the IOB includesadditional 512-byte blocks, these additional blocks (up to seven blocks)are also sequentially written into the current journal entry data fieldof the working copy. The I/O journal filter 282 also copies the valuesfrom the LayerID field 242, LBA/PageNum field 226, StoreID field 246,StoreLBA field 248, and In Time Stamp field 250 to the journal entryheader LayerID field 422, LayerLBA field 420, StoreID field 424,StoreLBA field 426, and TimeSeqID field 428 respectively. The value inthe Restricted field 432 is populated to indicate no restriction. Thevalue in the Clean 434 field is populated to indicate dirty or notclean. Finally the I/O journal filter 282 sets the value in theValidMask field 430 to reflect the blocks that have been or will beloaded into the journal entry data field. For example, if the IOBincludes five blocks of data, the I/O journal filter 282 would write thefirst of the five blocks of data into the first block of the journaldata entry field and the other four blocks into the immediatelyfollowing four blocks of the journal data entry field and establish thejournal header data based on the first block of data moved into thejournal data entry. In this example, the ValidMask field 430 would beset to “11111000”.

If the first 512-byte block of the currently active journal entry hasbeen written, the I/O journal filter 282 uses the value of the LayerIDfield 422 in the journal entry header, the value of the LayerLBA field420 in the journal entry header, and the value of the ValidMask field430 in the journal entry header to determine the values for the LayerIDand the layer LBA that should go in the next available 512-byte block ofthe journal entry data field. For instance, if the first block in thejournal entry data field contained data relating to a layer id of 0 anda layer LBA of 20 and the next available block was the second block inthe journal entry data field, the I/O journal filter 282 would concludethat the block of data for layer id 0 and layer LBA 21 should go in thesecond block in the journal entry data field. The calculated values forthe layer id and layer LBA are compared to the actual layer id and layerLBA values associated with next block of data associated with the IOB.If there is a match, the next block of data associated with the IOB iswritten into the next available 512-byte block of the journal entry datafield and the ValidMask field 430 is appropriately updated. To continuewith the example, if the 512-byte block of the IOB journal had a layerid of 0 and layer LBA of 21, the I/O journal filter 282 establishes the512-byte block of the IOB in the second 512-block of the journal entrydata field. If there is not a match and the currently active journalentry is not the last journal entry for the currently active journalpage, the currently active journal entry is incremented and the 512-byteblock associated with the IOB is written in the first block of the newactive journal entry. If there is not a match and the currently activejournal entry is the last journal entry for the currently active page(e.g., the working copy of the currently active journal page isfinished), the working copy of the active journal page is written to theactual journal 340 in the redundant and persistent store and a workingcopy of the next journal page is established in application memory.

If any write IOB has consumed, released, or modified a JE, the I/Ojournal filter 282 will update the journal table 352. Specifically, theI/O journal filter 282 obtains the value from the LayerLBA field 420 andthe value from the LayerID field 422. The I/O journal filter 282determines if there is an entry in the journal table (e.g., journaltable 352) that has the layer id and the layer LBA. If there is such anentry, the I/O journal filter 282 updates the Restricted field 432 ofthe currently active JE to indicate it is restricted. The I/O journalfilter 282 further updates the journal page and journal entry fieldswith the currently active journal page and currently active journalentry. If there is not an entry, the I/O journal filter 282 creates andentry in the table and enters the layer ID, layer LBA, journal page, andjournal entry values.

Generally, the I/O journal filter 282 operates with respect to IOBs inthe execution queue 314 that have SCSI read-related commands (read) thathave not been fully addressed by an intervening filter. Morespecifically, the I/O journal filter 282 obtains the value from theLayerID field 242 and the layer LBA value from the LBA/PageNum field226. The I/O journal filter 282 determines if there is an entry in thejournal table (e.g. journal table 352) that has the layer id and thelayer LBA. If there is such an entry, the block(s) of data that are thesubject of the read command are located in the journal at the journalpage and journal entry specified for the entry in the journal table thathas the noted layer id and layer LBA. The I/O journal 282 proceeds tothe specified journal entry, retrieves the LBA from the journal entryheader, determines the difference between the requested layer LBA andthe journal entry LBA to identify which of the 512-byte journal block(s)needs to be read. The I/O journal 282 causes the relevant block(s) tothen be read into memory store (e.g., memory store 52A or 52B) updatesthe DataSegmentVector field 240 to point to the location in memory storethat contains the read blocks. The I/O journal filter 282 places a“success” code in the error field 232 of the IOB and causes the IOB tostart propagating up the filter stack 132, thereby indicating that theSCSI read command of the IOB has been completed. If there is no entry inthe journal table for the specified layer id and layer LBA, the block(s)that are the subject of the SCSI read-related command are not in thejournal 340. In this case, the I/O journal filter 282 passes the IOB ondown the filter stack 132.

While the operation of the I/O journal filter 282 has been describedwith respect to 512-byte blocks and 2-megabyte pages, it should beappreciated that different block sizes can be employed in an effort tomatch the characteristics of the data to the characteristics of one ofthe stores among a group of stores in a data store system, the storeshaving different characteristics from one another. For example, thesizes of the blocks, data journal entry fields, and journal page caneach be varied to achieve this goal.

The I/O journal filter 282 is also capable of operating so as toimplement a dynamically tunable journal in which the order ofwrite-related commands in the execution queue 314 may be changed oraltered so as to realize data space and/or time-speed benefits orefficiencies relative to a data store, as described in greater detailbelow with regard to FIG. 9. To elaborate, the I/O journal filter 282receives the IOBs in the execution queue 314, analyzes a group of IOBsin the execution queue 314 to determine if changing the order of theIOBs will produce a data space and/or time-speed benefit. It should beappreciated that changing the order of the IOBs to attain a benefitresults in at least two IOBs that were separated by intervening IOBs inthe execution queue 314 being positioned closer to one another in thereordered group of IOBs. If the analysis shows that such a benefit wouldresult from reordering, the I/O journal filter 282 produces a reorderedgroup of IOBs. If, on the other hand, the analysis shows that no orlittle benefit would result from reordering the group of IOBs, theoriginal order of the group of IOBs remains unaltered. The I/O journalfilter 282 appends either the reordered group of IOBs or the group ofIOBs (e.g., the original unaltered group of IOBs) to the working copy ofthe currently active journal page. If the currently active journal entryis the last journal entry for the currently active page (e.g., theworking copy of the currently active journal page is finished), theworking copy of the active journal page is written to the actual journal340 in the redundant and persistent store and a working copy of the nextjournal page is established in application memory. As previously noted,this description relates to a single copy of the journal 340 that istypically located on is one of SSD 54A and SSD 54B. However, redundancyis provided by having two copies of the journal 340 with, in theillustrated embodiment, each copy of the journal 340 located on one ofSSD 54A and SSD 54B.

While the foregoing description of potentially reordering a group ofIOBs in the execution queue 314 based upon the identification of a dataspace and/or time-speed benefit, it should be appreciated that suchreordering can be precluded or limited in certain situations. Toelaborate, if the group of IOBs in the execution queue 314 includes IOBsthat overlap, e.g., are associated with same layer ID in the LayerIDfield 422 and operating on at least one layer LBA that is common to theLayerLBA fields 420 of at least two IOBs. For example, if a group ofthree IOBs in the execution queue 314 includes: (a) a first IOB has alayer ID of “3” in the LayerID field 422 and a layer LBA of “0” in theLayerLBA field 420, (b) a second IOB that has a layer ID of “2” in theLayerID field 422 and a layer LBA of “4” in the LayerLBA field 420, and(c) a third IOB that has a layer ID of “3” in the LayerID field 422 anda layer LBA of “0-1” in the LayerLBA field 420, the overlay of the firstand third IOBs limits the analysis of whether or not to reorder the IOBsto the first and second IOBs.

It should be appreciated that the analysis of a group of IOBs todetermine whether there is data space and/or time-speed benefit toreordering the IOBs can be implemented with respect to other datastores. The foregoing description of the analysis of a group of IOBsrelated to a group of IOBs in an execution queue 314 and related to thejournal 340, a copy of which is associated with each of the SSDs 54A,54B. The analysis can also be performed with respect to a group of IOBsassociated with the journal 340 and related to one or both of the RAIDdisk array 56A, 56B, which is further described below with respect tothe sorting or reordering to obtain contiguous blocks of data in thede-stage filter 370. Further, it should be appreciated that the analysisof a group of IOBs to determine if a data space and/or time-speedbenefit can be obtained can be applied to only one data store in a datastore system comprised on only one data store, all of the data stores ina data store system having multiple data stores, or to a subset of allof the data stores in a data store system having multiple data stores.

Background Filters

Generally, the group of background filters 164 operates to place data ona data store with performance characteristics that are commensurate withthe use of the data. For example, if a particular unit of data isfrequently read and/or written, the group of background filters endeavorto place such data on a store with a high-performance characteristics(e.g., low latency, high throughput, and high IOPS). Conversely, if aparticular unit of data is infrequently read and/or written, the groupof background filters endeavor to place such data on a store with lowerrelative performance characteristics. Moreover, to the extent thatplacing a unit of data requires moving the data from one store toanother store, the group of background filters 164 operates to move theunit of data in a manner that is speedy, conserves storage capacity, andhas a relatively small impact on the processing of IOBs directly relatedto an initiator. The group of background filters operate at the lowestcriticality within the primary data storage system 28 or with an allowedlatency that is significantly greater than the latency allowed in theforeground filters.

The background filters 164 operate in two contexts. The first contextinvolves the potential writing of data that is on one store to anotherstore. In the background filters 164, such potential movements areaccomplished using a super IOB that has a write-related SCSI blockcommand and facilitates communications between the filters. A super IOBis identical in form to IOB 182, except that the value of the PageModefield 224 is set to “on”, which means that the values in the LBA/PageNumfield 226 and the SectorCount/PageOffset field 228 now relate to pagesand not blocks. The second context involves the processing of an IOBthat has a SCSI read-related command that has not yet been fullyaddressed by any of the filters in the filter stack 132 that havepreviously processed the IOB.

Operation of the background filters 164 with respect to operations thatinvolve a super IOB is invoked by the I/O journal filter 282 indicatingthat a portion of the journal 340 is “dirty”, e.g., has not beenprocessed to determine whether data in the journal should be moved to adifferent store. The actual percentage of the journal that is “dirty” iscompared to a predetermined threshold value. If the actual percentage isless than the threshold percentage, operation of the background filters164 is not invoked with respect to super IOBs. If the actual percentageof the journal that is “dirty” has a triggering relationship withrespect to the threshold percentage (equals or exceeds, or onlyexceeds), operation of the background filters 164 is invoked for superIOBs. With respect to operations that involve an IOB with a SCSIread-related command, the presence of the IOB in the execution queue 314is detected and the operation of the background filters 164 is invoked.

The background filters 164 include a destage filter 370, advanceddeduplication filter 372, page pool filter 374, store converter filter376, and store statistics collection filter 378.

De-Stage Filter. Generally, the destage filter 370 operates to move databetween tiers of data stores with different characteristics and move thedata so that the characteristics of the data reflect the characteristicsof the store. In this regard, when the destage filter 370 is invokedbecause the percentage of the journal that is “dirty” has met somecriteria, the destage filter 370 operates to determine if one or morepages of contiguous data blocks can be assembled from data blocks thattypically are scattered throughout the journal. The destage filter 370also makes a determination as to what should happen to any data blocksthat cannot be assembled into a page.

If such a page can be assembled, the destage filter 370 generates asuper IOB and passes the super IOB down the filter stack 132. Thedestage filter 370 further assesses whether each of the blocks thatformed the page should, in addition to being the subject of the superIOB that will ultimately result in the blocks being written to anotherstore, be persisted in the journal (e.g., whether a block is being readfrequently enough to justify leaving the block in the journal). If twoor more blocks are to be persisted in the journal, the destage filter370 further assesses whether these blocks should remain in their currentlocations in the journal or be “compacted”, e.g., consolidated into oneor more consecutive journal entries. It should be appreciated that datafor any specific layer and layer LBA may persist in multiple stores ortiers simultaneously.

With respect to a data block or blocks that are in the journal and thatcannot be assembled into a page, the destage filter 370 operates toassess whether each such block has been resident in the journal for aperiod of time that exceeds a predefined threshold. If the threshold isexceeded, the destage filter 370 generates an IOB (not a super IOB) forthe data block or group of contiguous blocks that is less than a pageand passes the IOB down the filter stack 132. Further, the destagefilter 370 assesses whether the block(s) should be persisted in thejournal (e.g., whether the block(s) is being read frequently enough tojustify leaving the block in the journal). If two or more blocks are tobe persisted in the journal, the destage filter 370 further assesseswhether the blocks should remain in their current locations in thejournal or be “compacted”, e.g., consolidated into one or moreconsecutive journal entries. If the threshold is not exceeded, thedestage filter 370 assesses whether the two or more blocks of data thatare logically contiguous blocks that are separated from one another injournal but can be compacted into a single journal entry or journalpage. If not, the blocks remain in their current locations in thejournal.

With the foregoing background in mind, the destage filter 370 determinesif a page(s) can be assembled from the data blocks currently residing inthe journal 340. In this regard, the destage filter 370 makes a workingcopy of the current journal table (e.g. journal table 352) and sorts orreorders the entries in the copy of the journal table by layer id andlayer LBA. The destage filter 370 analyzes the sorted journal table and,if necessary, the ValidMask field 430 in the headers of one or morejournal entry headers 348 to determine if there is a layer with enoughconsecutive layer LBAs of the data block size to equal a page. Forexample, if the block size is 512-bytes and the page size is2-megabytes, 4096 consecutive blocks of data are required to assemble apage. If there are enough consecutive blocks of data to assemble a page,the destage filter 370 assembles a working page in a memory store(memory store 52A or 52B). A super IOB is generated and the IOB ispassed down the filter stack 132.

After the destage filter 370 assembles a page, the destage filter 370builds a super IOB 182 and populates certain fields of the IOB 182 withvalues from or derived from the journal 340. Specifically, the destagefilter 370 sets the command field 230 to block write command. If thedata is a full page, then the destage filter 370 sets the PageMode field224 of the IOB 182 as “on” to indicate that the IOB 182 initiallyrelates to a page and not a block or blocks of data. Moreover, the “on”value in the PageMode field 224 also indicates that the valuesestablished or to be established in the LBA/PageNum field 226 and SectorCount/PageOffset field 228 are PageNum and PageOffset values and not LBAand SectorCount values. The destage filter 370 uses data in the journalentry headers 348 to populate the LBA/PageNum field 226,Count/PageOffset field 228, LayerID field 242, StoreID field 246, andStoreLBA field 248. The destage filter 370 uses data in the journalentry headers 348 to establish values in the NumberOfDataSegments field236 and the DataSegmentVector field 238. To elaborate, the destagefilter 370 places the data from the journal blocks 351 into the memorystore (e.g., memory store 52A or 52B). The destage filter 370 places thenumber of data segments that are established in the memory store intothe NumberOfDataSegments field 236 and the address and length of each ofthe segments established in the memory into the DataSegmentVector field238. The destage filter 370 calculates a cyclic redundancy check (CRC)for each of the segments and places each of the CRC values in theDataCRCVector field 240. It should be appreciated that a dataverification techniques other that CRC can be employed in place of CRC.The value of the QoS Attributes field 244 is set to 0 or “lowestpriority”. If the values of the InitiatorID field 220, VolID field 222ErrorCode field 232, ErrorOffset field 234, IssuerStack field 252, andXtraContextStack field 254 are not automatically set to “null” orirrelevant values when the IOB 182 is first established, the destagefilter 370 establishes such values in these fields.

The destage filter 370 also pushes an indication onto the IssuerStackfield 252 of the IOB 182 that the destage filter 370 needs to doadditional processing when the IOB is propagating up the filter stack132.

The destage filter 370 also updates the Clean field 434 of the JE foreach journal entry that contributed one or more blocks to the page toindicate that the data associated with the journal entry is beingdestaged, e.g., is now the subject of a super IOB that will result inthe data being written to a different data store.

With respect to each of the data blocks that formed a page that is to bedestaged, the destage filter 370 makes a determination of whether or notto persist the data block on the journal 340. In this regard, thedestage filter 370 obtains statistical data from the statistics database168 for the layer ID and layer LBA associated with the block. If thestatistical data indicates that the data block is not being frequentlyread, the destage filter 370 removes the entry for the layer ID andlayer LBA in the journal table (e.g., journal table 352) and updatesClean field 434 to indicate that the data block has been evicted fromthe journal 340. This effectively frees up the JE for the data block foruse by the I/O journal filter 282.

If the statistical data indicates that the data block is beingfrequently read, the destage filter 370 makes a determination as towhether to leave the data block in its current location or compact thedata block with other data blocks that are being persisted. To make thisdetermination, the destage filter 370 assesses whether the journal pagethat contains the data block is sparsely populated or not. If thejournal page is sparsely populated and there is at least one other datablock associated with another sparsely populated journal page, thedestage filter 370 compacts the two data blocks into one journal page,thereby freeing up one journal page for use by the I/O journal filter282. If the journal page is not sparsely populated, the data block isallowed to remain in its current location in the journal 340.

If the destage filter 370 determines that: (a) a page could not beassembled from the data blocks resident in the journal 340 when thedestage filter 370 began processing the journal 340 (“unpageable datablocks”) or (b) the journal had data blocks that could be assembled intoa page (“pageable data blocks”) and unpageable data blocks, the destagefilter 370 processes each of the unpageable data blocks in the journalto assess how long the data block has been resident in the journal 340.In this regard, the destage filter 370 obtains the current time, obtainsthe “write” time from Time SeqID field 428 for the layer ID and thelayer LBA that relates to the data block to determine when the datablock was written into the journal 340, and determines the differencebetween the current time and the “write” time.

If the time difference exceeds a threshold, the destage filter 370creates an IOB (not a super IOB) for the data block and any contiguousdata blocks in a similar fashion to that noted for the super IOB butwith a PageMode value set to “off” and passes the IOB on down the filterstack 132. Additionally, the destage filter 370 makes a determination ofwhether or not to persist the data block on the journal 340. In thisregard, the destage filter 370 obtains statistical data from thestatistics database 168 for the layer ID and layer LBA associated withthe block. If the statistical data indicates that the data block is notbeing frequently read, the destage filter 370 removes the entry for thelayer ID and layer LBA in the journal table (e.g., journal table 352)and updates Clean field 434 to indicate that the data block has beenevicted from the journal 340. This effectively frees up the JE for thedata block for use by the I/O journal filter 282. If the statisticaldata indicates that the data block is being frequently read, the destagefilter 370 makes a determination as to whether to leave the data blockin its current location or compact the data block with other data blocksthat are being persisted. To make this determination, the destage filter370 assesses whether the journal page that contains the data block issparsely populated or not. If the journal page is sparsely populated andthere is at least one other data block associated with another sparselypopulated journal page, the destage filter 370 compacts the two datablocks into one journal page, thereby freeing up one journal page foruse by the I/O journal filter 282. If the journal page is not sparselypopulated, the data block is allowed to remain in its current locationin the journal 340.

If the difference between the write time and the current time does notexceed a threshold, the destage filter 370 makes a determination as towhether to leave the data block in its current location or compact thedata block with other data blocks that are being persisted. To make thisdetermination, the destage filter 370 assesses whether the journal pagethat contains the data block is sparsely populated or not. If thejournal page is sparsely populated and there is at least one other datablock associated with another sparsely populated journal page, thedestage filter 370 compacts the two data blocks into one journal page,thereby freeing up one journal page for use by the I/O journal filter282. If the journal page is not sparsely populated, the data block isallowed to remain in its current location in the journal 340.

The destage filter 370 queries the statistics database 168 to determineif the system has sufficient resources to process the destage. If thesystem does have sufficient resources, the destage filter 370 places an“In” time in the In Time Stamp field 250 that reflects the point in timewhen or about when the destage filter 370 passes the IOB 182 on down thefilter stack 132. If the system does not have resources to process thedestage IOB, then the destage filter pauses and then tries the statsdatabase query again.

Later, when a result IOB 182 is propagating up the filter stack 132 andreaches the destage filter 370, the current time is obtained, the “In”time stored in the In Time Stamp field 250 is obtained, and the totallatency associated with the processing of the IOB is calculated, e.g.,the elapsed time between when the “In” time value was obtained by thedestage filter 370 and the when the current time was obtained. Thedestage filter 370 updates layer tables in the statistics database 168with the total latency value. Additionally, the destage filter 370updates all JEs that correspond to the result IOB setting the bitmaskstate to destage complete.

When the destage filter 370 is invoked because there is an IOB with aSCSI read-related command, the destage filter 370 passes the IOB on downthe filter stack 132.

Advanced De-Duplication Filter. Generally, the advanced de-duplicationfilter 372 operates to preserve storage capacity at the primary datastorage system 28 by preventing blocks of data associated with a superIOB that are commonly written to the primary data storage system 28 anddo not have a readily calculable pattern from being written multipletimes such that each writing of the page consumes additional storagecapacity.

By way of background, the advanced de-duplication filter 372 maintains asuper dictionary table that is capable of holding a number of entriesthat is greater than the number of entries that the dictionary tableassociated with the dictionary deduplication filter 280 utilizes. Eachnon-null entry in the super dictionary table includes, for a pageassociated with a super IOB, a value for each of a cyclic redundancycheck (CRC) for the page, a layer ID, PageNum, a StoreID, and StoreLBA.The CRC is a number that is calculated using the data in a page andrepresentative of the data in a page but not necessarily a unique numberrelative to the data in the page, e.g., there is the possibility thattwo pages with different data have the same CRC. Nonetheless, if twopages of data do have the same CRC, there is a distinct possibility thatthe two pages do have the same data. It should be appreciated thathashes, checksums, and the like can be used in lieu of a CRC to identifypages that have potentially identical data.

With respect to the processing of a super IOB relating to a write, theadvanced deduplication filter 372 calculates a CRC for the page locatedin a memory store (memory store 52A or 52B) due to the operation of thedestage filter 370. The advanced deduplication filter 372 enters thecalculated CRC value and the values from the LayerID field 242,

PageNum field 226, StoreID field 246, and StoreLBA field 248 in thesuper dictionary table. The advanced deduplication filter 372 determinesif there is another entry in the super dictionary table that has thesame CRC value, the same value for the StoreID, and the value for theStoreID corresponds to a memory store. Two entries in the superdictionary table with the same CRC value are potentially identicalpages. Two entries in the super dictionary table that also each has avalue for the StoreID that corresponds to a memory store (which is ahigh speed memory) can be compared to one another very quickly. The dataassociated with the write IOB and the dictionary entry are both inmemory store 52A or 52B, the fastest type of store in the illustratedsystem. If there is another entry in the super dictionary table that hasthe same CRC value and a value for the StoreID that corresponds to amemory store, the advanced deduplication filter compares the two pagesto one another. If the two pages are identical, the advanceddeduplication filter 372 changes the value in the command field 230 ofthe super IOB from a write to a de-dup write, adjusts the values in theStoreID field 246 and StoreLBA field 248, and passes the super IOB ondown the filter stack 132.

Further, the advanced deduplication filter 372 increments a page counterthat is used to determine whether the identical page is being writtencommonly or frequently enough to warrant identifying the page as beingappropriate for use in the dictionary table used by the dictionarydeduplication filter 280 in the group of foreground filters 162. If thepage satisfies the test for inclusion in the dictionary table, theadvanced deduplication filter obtains the portion of the page (e.g., thesecond 64-bytes in the page) that is associated with each of thenon-null entries in the dictionary table. If the portion of the page isunique relative to each of the portions of the pages associated with theother entries, the page is added to the dictionary table. Further, ifthe dictionary table is full, the entry with the oldest access time(obtained from the statistic database 168) is deleted to make room forthe new entry. If the portion of the page is not unique relative to eachof the portions of the pages associated with the other entries in thedictionary table, the advanced deduplication filter 372 operates toidentify a portion of each of the pages in the dictionary table that isunique and updates the entire dictionary table accordingly. If a portionof each of the pages in the dictionary table that is unique cannot beidentified, the page is not added to the dictionary table.

If the two pages are not identical, the advanced deduplication filter372 proceeds to assess the impact of considering whether other entriesin the super dictionary table having the same CRC are duplicates of thepage associated with the super IOB. Specifically, the advanceddeduplication filter 372 queries the statistics database 168 todetermine if the QoS goals are currently being achieved or nearlyachieved (a “headroom” calculation). If the impact is acceptable, theadvanced deduplication filter 372 causes the page that is at thelocation identified by the values in the StoreID and StoreLBA fields inthe super dictionary table to be read into a memory store for comparisonto the page associated with the super IOB currently in the memory store.Since the page associated with the super IOB and the potentiallyidentical page are now both in memory, the comparison proceeds insubstantially the same fashion as described above when the two pageswere both in memory store when the processing of the super IOB by theadvanced deduplication filter 372 began. If the impact is notacceptable, the advanced deduplication filter 372 passes the super IOBon down the filter stack 132. If there is no entry in the superdictionary table that has the same CRC, the advanced deduplicationfilter 372 passes the super IOB on down the filter stack 132.

With respect to an IOB with a SCSI write-related command that does notrelate to a page, the advanced deduplication filter 372 deletes theentry in the super dictionary table that has the layer ID and thePageNum values set forth in the IOB. The entry is deleted because thewrite command associated with the IOB will be subsequently executed andlikely change the CRC for the page with which the data block(s) that arethe subject of the write command are associated. As such, the currentCRC for the page will no longer be valid and useable for assessingwhether there is a page that is the subject of a super IOB should bededuplicated. Further, the advanced deduplication filter 372 passes theIOB on down the filter stack 132.

Read De-Duplication Operation. Generally, the advanced deduplicationfilter 372 operates on an IOB having a SCSI read-related command thatneed not relate to a page to determine if the data associated with theidentified layer id and LBA is data that has been previouslyde-duplicated in the processing of an IOB with a SCSI write-relatedcommand relating to the same layer id and LBA. More specifically, theadvanced deduplication filter 372 obtains the value in the StoreID field246 and determines if the value is currently associated with thedictionary store 322. If the value is currently associated with thedictionary store 322, the advanced deduplication filter 372 then placesthe data from the dictionary store 322 into the memory store (e.g.,memory store 52A or 52B). The advanced deduplication filter 372 placesthe number of data segments that are established in the memory storeinto the NumberOfDataSegments field 236 and the address and length ofeach of the segments established in the memory into theDataSegmentVector field 238. Further, the advanced deduplication filter372 updates the value in the DataSegmentVector field to point to theaddress in the memory store (e.g., memory store 52A or 52B) that has thecopy of the dictionary page and, more specifically, to point the firstblock of the page that has the first block to which the SCSI readcommand relates. Further, the advanced deduplication filter 372 places a“success” code in the error field 232 and causes the IOB to startpropagating up the filter stack 132, thereby indicating that the SCSIread-related command of the IOB has been completed. If the value in theStoreID field 246 is not currently associated with the dictionary store322, the IOB is passed down the filter stack 132 for further processing.

Page Pool Filter. Generally, the page pool filter 374 operates toallocate storage space on the stores associated with the primary datastorage system 28 other than a store that is non-persistent and anyportion of a store that is not dedicated to a journal as needed. Morespecifically, the page pool filter 374 maintains a store map for eachstore for which the filter can allocate storage that identifies all ofthe storage pages on the store and indicates whether or not each suchstorage page has been allocated. Additionally, the page pool filter 374maintains a layer-store table 410 with each entry in the table mapping alayer ID and layer LBA to a StoreID and StoreLBA. The table alsoindicates whether the data at a particular StoreID and StoreLBA isshared by more than one layer ID, layer LBA. This indication is referredto as a ref-count, with a ref-count of 1 indicating that the data at thelocation specified by the StoreID and StoreLBA is only associated withone layer ID, layer LBA. A ref-count that is greater than 1 indicatesthat the data at the location specified by the StoreID and Store LBA isassociated with more than one layer ID, layerLBA.

With the foregoing background in mind, the page pool filter 374 operateson a received IOB to determine if the received IOB is an IOB or a superIOB. More specifically, the page pool filter 374 obtains the value inthe PageMode field 224 of the received IOB. If the value is “yes”, thereceived IOB is a super IOB, e.g., embodies a write-related command thatinvolves a page of data.

With respect to a super IOB, the page pool filter 374 determines whetherthe command in the command field 230 is a write command or a dedup writecommand. If the command is a write command, the page pool filter 374obtains the values in the LayerID field 242 and the LBA/PageNum field226 and determines whether there is an entry in the layerstore table410. If there is no entry in the layer-store table 410 with thespecified layer ID and layer LBA values, the page of data for thespecified layer ID and layer LBA has not been previously written to anyof the stores for which the page pool filter 374 allocates space. Inthis case, the page pool filter 374 interrogates the store map(s) toidentify a page of space on the related store to which the page of datacan be efficiently written. With respect to an identified page, the pagepool filter 374 determines the values for the StoreID and StoreLBA. Thepage pool filter 374 allocates the page to the layer ID and layer LBA.In this regard, the page pool filter 374 updates the layer-store tableto include an entry with the values for the layer ID, layer LBA, StoreIDand StoreLBA and stores the updated store map. Further, the page poolfilter 374 sets the ref-count field in the entry to 1 to indicate thatthe data to be established beginning at the location specified by theStoreID and StoreLBA values is currently associated with only one layerID and layer LBA. The page pool filter 374 updates the StoreID field 246and StoreLBA field 248 in the IOB with the StoreID and StoreLBA valuesof the allocated storage. The updated super IOB is then passed down thefilter stack 132.

If there is an entry in the layer-store table 410 with the specifiedlayer ID and layer LBA values, data associated with the specified layerID and layer LBA has been previously written to a store. With respect tosuch data, the page pool filter 374 determines if the data is shared,e.g., associated with another layer ID and layer LBA values. In thisregard, the page pool filter 374 determines if the ref-count field inthe entry in the layer-store table 410 for the layer ID and layer LBA inthe super IOB is 1. If the ref-count is 1, the data at the locationspecified by the StoreID and StoreLBA values in the table is not shared.In this case, the values for the StoreID and StoreLBA in the table arerespectively loaded into the StoreID field 246 and StoreLBA field 248.The updated super IOB is then passed on down the filter stack 132.

If the ref-count is greater than 1, the data at the location specifiedby the StoreID and StoreLBA for the entry in the layer-store table 410is shared with at least one other layer ID and layer LBA. In this case,because the data at the location is shared and the IOB involves thewriting of data that is different than the data currently at thelocation, the page pool filter 374 must allocate new space on a storefor the page of data associated with the super IOB. In this regard, thepage pool filter 374 proceeds substantially as noted with respect to thesituation in which there was no entry in the layer-store table 410 withthe specified layer ID and layer LBA values. Further, the page poolfilter 374 also decrements the ref-counts.

If the command in the command field 230 of the super IOB is a dedupwrite, the page pool filter 374 establishes a new entry in thelayer-store table 410 and populates the entry with the values from theLayerID field 242, LBA/PageNum 226 field 226, StoreID field 246, and theStoreLBA field 248 from the super IOB. In this instance, the values inthe StoreID field 246 and the StoreLBA field 248 were previouslyestablished by the advanced deduplication filter 372. Further, the pagepool filter 374 identifies the other entries in the layer-store table410 that have the same value for the StoreID and StoreLBA. With respectto each of these entries in the layer-store table 410 the ref-countvalue is incremented. The page pool filter 374 also establishes thisincremented ref-count value in the new entry in the layerstore filter.The processing with respect to this super IOB is now complete.Consequently, the page pool filter 374 places a “success” code in theerror code field 232 and causes the IOB to start propagating up thefilter stack 132.

If the received IOB is not a super IOB, the page pool filter 374determines whether the command in the command field 230 is a writecommand or a read command. If the command is a write command, the pagepool filter 374 obtains the values in the LayerID field 242 and theLBA/PageNum field 226 and determines whether there is an entry in thelayer-store table 410. If there is no entry in the layer-store table 410with the specified layer ID and layer LBA values, the block(s) of datafor the specified layer ID and layer LBA has not been previously writtento any of the stores for which the page pool filter 374 allocates space.In this case, the page pool filter 374 interrogates the store map(s) toidentify a page of space on the related store to which the block(s) ofdata can be efficiently written. With respect to an identified page, thepage pool filter 374 determines the values for the StoreID and StoreLBA.The page pool filter 374 allocates the page to the layer ID and layerLBA. In this regard, the page pool filter 374 updates the layer-storetable 410 to include an entry with the values for the layer ID, layerLBA, StoreID and StoreLBA and stores the updated store map. Further, thepage pool filter 374 sets the ref-count field in the entry to 1 toindicate that the data to be established beginning at the locationspecified by the StoreID and StoreLBA values is currently associatedwith only one layer ID and layer LBA. The page pool filter 374 updatesthe StoreID field 246 and StoreLBA field 248 in the IOB with the StoreIDand StoreLBA values of the allocated storage. The update IOB is thenpassed down the filter stack 132.

If there is an entry in the layer-store table 410 with the specifiedlayer ID and layer LBA values, data associated with the specified layerID and layer LBA has been previously written to a store. With respect tosuch data, the page pool filter 374 determines if the data is shared,e.g., associated with another layer ID and layer LBA. In this regard,the page pool filter 374 determines if the ref-count field in the entryin the layer-store table 410 for the layer ID and layer LBA in the IOBis 1. If the ref-count is 1, the data at the location specified by theStoreID and StoreLBA values in the layer-store table 410 is not shared.In this case, the values for the StoreID and StoreLBA in the layer-storetable 410 are respectively loaded into the StoreID field 246 andStoreLBA field 248. The super IOB is then passed on down the filterstack 132.

If the ref-count is greater than 1, the data at the location specifiedby the StoreID and StoreLBA for the entry in the layer-store table 410is shared with at least one other layer ID and layer LBA. In this case,because the data at the location is shared and the IOB involves thewriting of data that is different than the data currently at thelocation, the page pool filter 374 must allocate new space on a storefor the page of data associated with the super IOB. Moreover, becausethe writing to the store is page-based and not block-based at this pointand the IOB relates to a block(s) and not a page, the page pool filter374 must build the page that is to be written to the newly allocatedspace. Consequently, the page pool filter 374 reads the page that is atthe location specified by the current StoreID and StoreLBA in thelayer-store table 410 into a memory store (e.g., memory stores 52A or52B) and modifies the page to include the block(s) that are associatedwith the IOB. The page pool filter 374 establishes a new entry in thelayer-store table 410 and enters the values from the LayerID field 242and LBA/PageNum field 226 of the IOB into the new entry in the table.Further, the StoreID and StoreLBA values for the newly allocated spaceare also placed in the new entry. The ref-count for the new entry is setto 1 to indicate that the page is not shared with any other layer ID andlayer LBA. The page pool filter 374 updates the values of the StoreIDfield 246 and the StoreLBA field 248 in the IOB to reflect the StoreIDand StoreLBA for the newly allocated space. Further, the page poolfilter 374 updates the DataSegmentVector 240 in the IOB to indicate thelocation of the modified page in the memory store. The updated IOB isthen passed down the filter stack 132.

If the command is a read command, the page pool filter 374 uses thevalues from the LayerID field 242 and the LBA/PageNum field 226 toidentify the entry in the layerstore table 410 that relates to the datathat is to be read. In this regard, the value in the LBA/PageNum field226 relates to an LBA and not a page. The page pool filter 374accomplishes the conversion by masking off certain bits of the LBAvalue. The layer ID and PageNum values are then used to identify theentry in the layer-store table 410 relating to the data that is thesubject of the read command. The page pool filter 374 retrieves thevalues for the StoreID and StoreLBA associated with the entry in thelayer-store table 410 and loads these values into the StoreID field 246and StoreLBA fields 248 of the IOB. The updated IOB is then passed downthe filter stack 132.

Store Converter Filter. Generally, the store converter filter 376processes super IOBs and IOBs so as to generate an element specificIOB(s), e.g., the command(s) that are needed to actually perform theread or write of the data associated with the super IOB or IOB. Toelaborate, a particular store has data transfer requirements, a dataredundancy attribute, and a path redundancy attribute. The storeconverter filter 376 processes super IOBs and IOBs to produce theelement specific IOB(s) with the command(s) to the store that satisfythe data transfer requirements of the store, preserve the dataredundancy attribute of the store, and preserve the path redundancyattribute of the store.

Write Data Transfer—Size. With respect to super IOBs and IOBs that haveSCSI write-related commands, the store converter filter 376 interrogatesa store table to obtain the size of a write-related data transfer thatthe store accommodates. If the size of the data transfer accommodated bythe store is equal to a page, the store converter filter 376 generatesthe element specific IOB with the command(s) necessary to write the pageof data associated with the super IOB to the store.

With respect to a super IOB with a write-related command, if the size ofthe data transfer accommodated by the store is greater than a page, thestore converter filter 376 generates the element specific IOB(s) withthe command(s) necessary to: (a) read the current greater portion ofdata that is on the store and that includes the location at which thepage is to be written, (b) modify the read current greater portion ofdata to include the page of data associated with the super IOB, and (c)write the modified greater portion of data to the store. For example, ifthe store requires that write data transfers be done in 4-megabytechunks, the store converter filter 376 generates the commands necessaryto: (a) read the current 4 megabyte chunk of data on the store thatincludes the location at which the page associated with the super IOB isto be written, (b) modify the read 4-megabyte chunk to include the pageassociated with the super IOB, and (c) write the modified 4-megabytechunk to the store.

Conversely, if the size of data transfer accommodated by the store isless than a page, the store converter filter 376 divides the page ofdata associated with the super IOB into whatever size chunks of data arerequired by the store and generates the element specific IOB(s) with thecommand(s) for transferring these chunks of data to the store. Forinstance, if a store requires that data to be written in 512-bytechunks, the store converter filter 378 divides the 2-megabyte pageassociated with the super IOB into 4096 512-byte chunks and generatesthe command(s) for writing each of the 4096 512-byte chunks to thestore.

If the size of data transfer accommodated by a store is greater than apage but not a whole number multiple of a page, the store converterfilter 376: (a) divides the page into one or more chunks of the sizerequired by the store and generates the command(s) for writing each ofthese chunks to the store and (b) with respect to the remaining datathat is less than the size of data transfer accommodated by the store,produces the read, modify, write commands previously described forwriting the data to the store.

With respect to an IOB with a SCSI write-related command, the storeconverter filter 376 operates in substantially the same fashion as notedwith respect to a super IOB, except that the size of the block or blocksof data that are the subject of the IOB rather than a page are comparedto the size of the data transfer accommodated by the store.

Write—Data Redundancy. The store converter filter 376 also interrogatesthe store table to determine the value of the data redundancy attributeassociated with the store, performs any calculations that are associatedwith satisfying this attribute for the store, and generates or modifiesthe element specific IOB so as to implement the data redundancy. Forexample, if a store is comprised of a RAID-6 element, the storeconverter filter 376 engages in the parity calculations that are neededfor use with a store that includes such an element and modifies theelement specific IOB accordingly. As another example, if the storeincludes two elements that are mirrored to provide data redundancy, thestore converter filter 376 modifies the element specific IOB to includethe command(s) needed for implementing the mirroring.

Write—Path Redundancy. The store converter filter 376 furtherinterrogates the store table to determine the value of the pathredundancy attribute associated with the store. In addition, the storeconverter filter 376 interrogates a configuration table for the primarydata storage system 28 that provides the physical layout of the leveland the characteristics of the various elements at the level. Forexample, the configuration table identifies each store, the number ofI/O ports associated with each store, the status of the ports,identifies the switches in the store and the status of the switches etc.The store converter filter 376 generates or modifies the elementspecific IOB to provide the necessary information for routing the datafrom its current location in the primary data storage system 28 (e.g.,the memory store) to the store.

Write—Element Specific IOB. With respect to either an IOB or a super IOBwith a SCSI write-related command, once the assembly of the elementspecific IOB is complete, the store converter filter 376 pushes anindication onto the IssuerStack field 252 that the store converterfilter 376 needs to conduct further processing of the super IOB or IOBafter the execution or attempted execution of the commands in theelement specific IOB is complete. The store converter filter 376 passesthe element specific IOB on down the filter stack 132.

Read Data Transfer—Size. With respect to an IOB with a SCSI read-relatedcommand, the store converter filter 376 interrogates a store table toobtain the size of a read-related data transfer that the storeaccommodates. If the size of the read data transfer accommodated by thestore is equal to the size of the data that is the subject of the IOB,the store converter filter 376 generates the element specific IOB withthe command(s) necessary to read the data associated with the IOB fromthe store.

If the size of a data transfer accommodated by the store is greater thansize of the data that is the subject of the IOB, the store converterfilter 376 generates the element specific IOB with the command(s)necessary to read the current greater portion of data that is on thestore and that includes the location with the data that is the subjectof the IOB into the memory store. The store converter filter 376 thenupdates the value in the DataSegmentVector field to point to the addressin the memory store (e.g., memory store 52A or 52B) that has the copy ofthe page and, more specifically, to point the first block of the pagethat has the first block to which the SCSI read command relates.

If the size of data transfer accommodated by the store is less than thesize of the data associated with the IOB, the store converter filter 376determines the number of data transfers that will be necessary totransfer data of the size specified in the IOB and generates the elementspecific IOB(s) with the command(s) for conducting the calculated numberof reads from the store.

If the size of a data transfer accommodated by a store is less than thesize of the data associated with the IOB but not a whole number multipleof a size of the data, the store converter filter 376: (a) determinesthe number of data transfers that will be necessary to transfer data ofthe size specified in the IOB and generates the element specific IOB(s)with the command(s) for conducting the calculated number of reads fromthe store and (b) with respect to the remaining data that is less thanthe size of data transfer accommodated by the store, generates ormodifies the element specific IOB to include the command(s) necessary toread the portion of data that is on the store that is of a greater sizethan the remaining data but includes the location with the remainingdata.

Read—Data and Path Redundancy. The store converter filter 376 accesses ahardware state table to determine which path(s) and element(s) to whichthe element specific IOB should be sent.

Read—Element Specific IOB. With respect to either an IOB or a super IOBwith a SCSI read-related command, once the assembly of the elementspecific IOB is complete, the store converter filter 376 pushes anindication onto the IssuerStack field 252 that the store converterfilter 376 needs to conduct further processing of the super IOB or IOBafter the execution or attempted execution of the commands in theelement specific IOB is complete. The store converter filter 376 passesthe element specific IOB on down the filter stack 132.

Later, when a result IOB 182 is propagating up the filter stack 132 andreaches the store converter filter 376, the store converter filter 376updates store hardware stats tables in the statistics database 168 withthe latency value, throughput, queue depth, and use count. It should beappreciated that other tables or statistics in the statistics database168 may also be updated.

Store Stats Collection Filter. Generally, the store stats collectionfilter 378 operates to collect certain store and element relateddata/statistical information for each IOB passed to the store statscollection filter 378 from the store convertor filter 376 when the IOBis going down the filter stack 132. To elaborate with respect to IOB182, the store stats collection filter 378 processes the IOB 182 toobtain the store id from the StoreId field 246, the element id from theElementID field 256, the sector count from the SectorCount/PageOffsetfield 228, and the “In” time stamp value from the In Time Stamp field250. The store stats collection filter 378 also obtains the current timefrom the operating system. The store stats collection filter 378 usesthe value of the “In” Time Stamp and the current time to calculate thelatency that the IOB has experienced between when the “In” Time Stampvalue was established in the destage filter 370 and when the currenttime is obtained by the store stats collection filter 378 (hereinafterreferred as “first latency”). The store stats collection filter 378communicates with the statistics database 168 so as to: (a) update atable for the store that is maintained in the database to reflect thatan IOB associated with the store will be processed that has the sectorsize obtained from the IOB and that the IOB has experienced thecalculated first latency and (b) update a table for the element that ismaintained in the database to reflect that an IOB associated with theelement will be processed that has the sector size obtained from the IOBand that the IOB has experienced the calculated first latency.

The store stats collection filter 378 also pushes an indication onto theIssuerStack field 252 of the IOB 182 that the store stats collectionfilter 378 needs to do additional processing when the IOB is propagatingup the filter stack 132. Further, the store stats collection filter 378also pushes the current time onto the XtraContextStack field 254.

Later, when the IOB 182 is propagating up the filter stack 132 andreaches the store stats collection filter 378, the store statscollection filter 378 obtains the time from the XtraContextStack field254 (which is no longer the current time), obtains the “new” currenttime, and calculates a second latency, e.g., the elapsed time betweenwhen the time value was obtained that was pushed onto theXtraContextStack field 254 and the IOB was propagating down the filterstack 132 and the when the “new” current time was obtained. The storestats collection filter 378 updates the store and element tables in thestatistics database 168 with the second latency value.

Storage Hardware Driver. Generally, the storage hardware driver 380controls a SCSI card so as to produce the electrical signals needed toreceive a message, such as SCSI block result, and transmit a message,such as a SCSI block request. The storage hardware driver 380 assuresthe addressing of packets associated with a message. With respect toreceived packets, the storage hardware driver 380 confirms that each ofthe received messages does, in fact, belong to the SCSI card. Withrespect to messages that are to be transmitted, the storage hardwaredriver 380 assures that the each message is appropriately addressed sothat the message gets to the desired element. With respect to a receivedmessage, the storage hardware driver 380 also recognizes the packet asrequiring further routing back up the filter stack 132. The storagehardware driver 380 also performs other processing in accordance withthe protocols, e.g., ordering packets, checksum etc.

It should be appreciated that the storage hardware driver 380, operatesto process block commands, e.g., commands that relate to the reading ofa block data from or writing of a block data to a storage medium. Assuch, the storage hardware driver 380 can be adapted to operate withstorage hardware other that SCSI cards.

It should be appreciated that a number of functions noted with respectto the primary data storage system 28 can be realized with a primarydata storage system having a single storage processor and a single datastore and primary data storage systems having more elements than notedwith respect to the primary data storage system 28. For example, thetiering function described with respect to I/O journal filter and thedestage filter can be practiced in a primary data system with two datastores having different performance characteristics. The QoS functiondescribed with respect to the QoS filter can be practiced in a primarydata storage system that has a single data store where there are two aremore volumes associated with the store. The de-duplication function canbe practiced in a primary data storage system with a single data store.It should also be appreciated that the redundancy described with respectto the primary data storage system 28 is not required to practice manyof the functions provided by the filters in the filter stack. It shouldalso be appreciated that a primary data storage system can employ afilter stack with a fewer number or greater number of filters than arein the filter stack 132. For instance, in a primary data storage systemthat is only going to service a single volume, a filter stack can beemployed that omits a QoS filter. Additionally, a filter stack can beemployed in which the order of filters in the stack are different thanin filter stack 132. For instance, a filter stack could be employed inwhich an I/O journal filter preceded a dictionary deduplication filter.

Tier and Tiering. A tier is a group of stores that have similarcharacteristics such as throughput, latency, capacity, path redundancy,data redundancy, and atomic block size (e.g., the smallest individuallyaddressable block of a store) or a store with a defined set of suchcharacteristics. For example, memory store 52A and 52B comprise a tier,RAID disk array 56A and 56B comprise a different tier, and SSDs 54A and54B comprise yet another tier. One tier can differ from another tier inone characteristic or multiple characteristics. For instance, aparticular tier may have specific latency and throughput characteristicswhile another tier may have the same latency but a different throughputcharacteristic.

A tiering storage system is a storage system that attempts to match theaccess pattern relating to a block of data in the system to the tierhaving the most appropriate or compatible characteristics.

Many of the filters in the filter stack 132 are involved in providingtiering functionality, e.g., the QoS filter 274, the patternde-duplication filter 278, the dictionary deduplication filter 280, theI/O journal filter 282, the destage filter 370, the advanceddeduplication filter 372, the page pool filter 374, the calculationengine 320, the dictionary store 322, and the statistics database 168.

The QoS filter 274 evaluates an IOB and volume, criticality, andhardware statistics from the statistics database 168 to determine themost compatible and available tier(s) for the blocks of data relating toan IOB. The QoS filter 274 updates the AllowedStores field 260B of theIOB with the identified tier(s). It should be appreciated that theAllowedStores field 260B can be implemented as a bitmask and the QoSfilter 274 can indicate in the bitmask that an IOB should skip a tier.For example, in the case of a very large write data related command, theQoS filter 274 might indicate that the write data associated with theIOB be written to the RAID disk array 56A or 56B instead of the SSDs 54Aor 54B, which are in a higher tier than the RAID disk arrays 56A, 56B.

The pattern de-duplication filter 278 and the calculation engine 320implement a tier-1 (the fastest tier, but with a limited capacity)functionality in the illustrated primary data storage system 28. Thepattern de-duplication filter 278 operates to identify and respond toIOBs that contain blocks of data capable of being stored or retrievedfrom the calculation engine 320 or other similar engines. Thecalculation engine 320 provides a CPU store for storing and retrievingblocks of data that are readily calculable. The calculation engine 320is implemented by using a CPU and a limited amount of high speed memoryto store and retrieve blocks of data. The calculation engine has a blocksize characteristic of 512 bytes (the smallest of any tier). Thecalculation engine 320 has the lowest latency and highest bandwidth ofthe stores illustrated. It should be appreciated that the calculationengine 320 could be realized using specialized hardware such as a DMAengine or an MMX processor.

The dictionary de-duplication filter 280 and the dictionary store 322implement a tier-2 (slower than tier-1 but with greater capacity thantier-1) functionality. The dictionary de-duplication filter 280 operatesto identify and respond to IOBs that contain blocks of data that areidentical to the blocks of data stored in the dictionary store 322. Thedictionary store 322 provides a dictionary table and a memory store 52Aor 52B for storing and retrieving blocks of data which are not readilycalculable. The dictionary store 322 has a block size characteristic of2 MB.

The I/O journal filter 282 and the SSDs 54A and 54B implement a tier-3(slower than tier-2 but with greater capacity than tier-2)functionality. The I/O journal filter 282 operates to identify andrespond to IOBs that the filters above in the filter stack 132 have notfully processed. The I/O journal filter 282 stores blocks of data to andretrieve blocks of data from the SSDs 54A and 54B based upon thecharacteristics of the SSDs 54A and 54B (e.g. atomic block size,performance, throughput, IOPs, persistence, and redundancy). The SSDs54A and 54B each provide a persistent store for storing blocks of data.The SSDs 54A and 54B each have an atomic block size characteristic of 4KB.

The destage filter 370 is responsible for movement of blocks of databetween two tiers. The destage filter 370 decides when blocks of datarelating to an IOB should be copied, moved, or cleared relative tomultiple tiers (in the illustrated system 28, the tier-3 SSDs 54A or 54Band the tier-4 RAID disk array 56A or 56B). The destage filter 370 usesthe characteristics of the source and destination tiers to accommodatethe different tier requirements. For example, the SSDs 54A and 54Brequire atomic block accesses to be 4 KB in size while the RAID diskarray 56A and 56B require atomic block accesses to be 2 MB (page size).Thus, destage filter 370 executes a multitude of reads from the SSDs 54Aor 54B in 4 KB chunks that coalesce in high speed memory until 2 MB havebeen read. The destage filter 370 then executes a write command to theRAID disk array 56A or 56B with the 2 MB that is now in high speedmemory. Likewise, the destage filter 370 evaluates other characteristicsof the various stores and accommodates the characteristic strengths andattempts to avoid the characteristic weaknesses. For example, the RAIDdisk array 56A or 56B has a seek penalty. Due to this penalty, thedestage filter 370 processes IOBs in a fashion to limit or reduce thisseek penalty impact. The ability of destage filter 370 to accommodatevarious characteristics of different stores enables more efficient useof resources. For example, the atomic block size of the SSDs 54A and 54Bis smaller than the atomic block size of the RAID disk array 56A or 56Bwhich allows the SSDs 54A and 54B to contain smaller segments of morefrequently accessed blocks of data and not require the SSDs 54A and 54Bto hold blocks of data that are adjacent to the frequently accessedblocks of data. In effect this is more efficient use of the SSDs 54A and54B.

The destage filter 370 can also copy blocks of data between tiers so asto maintain a block of data in multiple tiers and thus increasingredundancy associated with the block of data. This also allows the blockof data that is located in multiple tiers to be “fast reused”. Fastreuse occurs when a tier includes a copy of a block(s) (e.g., there isanother copy in another tier) and it is necessary to make space in thetier for a block or blocks of data associated with a different IOBcommand. In this case, the copy of the block(s) in the tier can bedeleted/written over to make space for the block(s) associated with thedifferent IOB command.

The destage filter 370 endeavors to match a block or blocks of relateddata to the tier that is appropriate for the access pattern associatedwith the block or blocks of related data. To accomplish this, thedestage filter 370 accesses the statistics database 168 to acquirehistorical statistics related to the volume with which the data block orrelated data blocks are associated and evaluates those statistics todetect trends in the access pattern. For example, if the initiatoraccess pattern is a streaming video (a trend represented by a sequenceof consecutive IOBs), the destage filter 370 would likely direct theblocks of data to the tier containing the RAID disk array 56A or 56Bbecause the RAID disk array 56A or 56B is more efficient than othertiers in processing large, contiguous blocks of data. In contrast, ifthe initiator access pattern is a random read, the destage filter 370endeavors to maintain the blocks of data in a tier such as SSDs 54A and54B because this tier has a smaller seek latency penalty relative to theother tiers in the system.

The advanced de-duplication filter 372 provides movement of blocks ofdata between tier-4 and tier-2. More specifically, advancedde-duplication filter 372 uses the super dictionary table to determinewhen a group of contiguous blocks of data that constitute a page isfrequently accessed. If a page is accessed more frequently than otherpages active in the dictionary table, then the advanced de-duplicationfilter 372 identifies that page as a candidate for movement to tier-2.The advanced de-duplication filter 372 subsequently coordinates with thedictionary de-duplication filter 280 to update the dictionary table withthe candidate page.

The page pool filter 374 and the RAID disk array 56A or 56B implement atier 4 (slower than tier-3 but with greater capacity than tier-3)functionality. The page pool filter 374 operates to store and retrieveblocks of data from RAID disk array 56A and 56B considering thecharacteristics of RAID disk array 56A and 56B.

It should be appreciated that tiering functionality can be implementwith other combinations of filters and stores. It should also beappreciated that other filter stack 132 layouts could generate differenttier assignments than those listed above. Additional storage types suchas the cloud storage provider 64 or tape stores would likely involve thefilter stack 132 adding additional filters or re-arranging the order ofthe filters in such a way as to accommodate the characteristics of anynew tier employing one or more of these types of stores. Further, asfaster stores become available, these faster stores can be used toimplement a tier that is faster than the memory that constitutes thetier-1 in the illustrated system.

FIG. 9 depicts one embodiment of a management module 900. In general,the management module 900 may manage or tune operations for the journal340. In one embodiment, the management module 900 may reorder IOBs orother storage commands by storage volume, by snapshot version or layer,or the like. The management module 900, in a further embodiment, mayadjust a frequency of writing data from a write buffer (e.g., thevolatile memory 52, an execution queue 314, or the like) based on a rateof write requests or the like. The management module 900, in certainembodiments, may adjust a ratio of storage capacity for storing mirroredwrite data to storage capacity for storing non-mirrored read data, in adata store 48 or the like (e.g., a journal 340, a solid-state device 54,a hard disk drive 56, or the like).

The management module 900, in certain embodiments, may be part of or incommunication with the filter stack 132 or the like. For example, themanagement module 900 may comprise a foreground filter 162, a backgroundfilter 164, or the like, may be part of or in communication with the IOjournal filter 282, the layer map filter 272, the destage filter 370, orthe like. In the depicted embodiment, the management module 900 includesa receiver module 902, an order module 904, a buffer module 906, ajournal module 908, a destage module 910, and a region management module912.

In one embodiment, the receiver module 902 is configured to monitorand/or receive IOBs or other storage commands. As used herein, a storagecommand comprises a request or message to perform a predefined actionwith regard to data associated with the storage command and/or a recordof the predefined action once it has been performed. A write commandcomprises a request, message, or record of data to be written for alogical ID such as a logical identifier, a range of logical identifiers,a file, an object, or the like. A storage command (e.g., a writecommand, a read command, or the like) may include metadata associatedwith the command and/or data of the storage command, as described abovewith regard to IOBs.

Metadata, as used herein, comprises information (e.g., controlinformation, statistical information, labels, identifiers, parameters,or the like) describing other data, such as a storage command, data of astorage command, or the like. Metadata may include a field or header ofan iSCSI encapsulation packet 180, a field of an IOB 182, QoS attributes244, a volume ownership table 286, a volume information table 292, ajournal page header 344, a journal entry header 348, a journal table352, a layer store table 410, or the like. In certain embodiments, anIOB, a journal page header 344, a journal entry header 348, a journaltable 352, or other metadata for a storage command includes a marker orindicator of an order of operations, such as a sequence identifier, atimestamp, an ordered list, a monotonically increasing number or value,or the like, such as the InTimeStamp 250 described above. In otherembodiments, an order of storage commands in a journal 340 may providean order of operations, without a separate marker or indicator. Asdescribed in greater detail below, the order module 904 may beconfigured to honor or enforce an order of operations for storagecommands for the same storage volume, for the same snapshot or snapshotversion, or the like, while reordering storage commands for differentstorage volumes, for different snapshots or snapshot versions, or thelike.

A storage command such as a write command, a read command, or the like,may include an IOB, a storage request (e.g., a write request, a readrequest, a TRIM request), a block command, a SCSI command, or the like.The receiver module 902, in certain embodiments, may monitor a certaintype or types of storage commands, such as just write requests, justread requests, write requests and read requests, or the like.

The receiver module 902, in one embodiment, may monitor and/or receivestorage commands from a user computer 34, 36, an initiator 38, a storageclient, an application, an operating system, a user, or the like. Thestorage commands may be for different storage volumes, differentsnapshots, different versions or layers of a snapshot, different qualityof service levels, or the like. The receiver module 902, in certainembodiments, may monitor and/or determine a rate at which storagecommands are received, such as a rate at which write requests arereceived, a rate at which read requests are received, a rate at whichread requests and write requests are received, or the like. As describedabove, IOBs or other storage commands and associated data may berecorded or stored in a journal 340 data structure, stored in asolid-state drive 54 or the like for later destaging to a hard diskdrive 56 or other backing store. The receiver module 902, in cooperationwith the buffer module 906 or the like, may buffer or store storagecommands and/or associated data in volatile memory 52, in an executionqueue 314, or the like, to group or gather multiple storage commands forexecution at once, as a write combine buffer or the like.

As used herein, a write combine buffer may comprise volatile ornon-volatile memory or storage used to queue, buffer, or store multiplewrite commands and/or associated data for writing or executing together,instead of separately. The receiver module 902 and/or the buffer module906, in certain embodiments, may use a volatile memory 52, an executionqueue 314, volatile memory of a host device 34, 36, 38, or the like as awrite combine buffer for a journal 340. In a further embodiment, thejournal module 908 may use a journal 340, a solid-state storage device54, or the like as a write combine buffer for a hard disk drive 56 orthe like. The receiver module 902 and/or the buffer module 906, incertain embodiments, may buffer or queue received write commands orother storage commands in a time sequence order (e.g., an order in whichthe write commands are received).

In one embodiment, the order module 904 adjusts, reorders, or groupsstorage commands received, queued, and/or buffered by the receivermodule 902 and/or the buffer module 906. The receiver module 902 mayreceive storage commands in a sequential or chronological order, by time(e.g., the original time sequence order described above). A timesequence order for storage commands, as used herein, comprises achronological arrangement or sequence of storage commands, in relationto each other, in which the storage commands were sent and/or received.The order module 904 may change or rearrange the received storagecommands out of the sequential, chronological, time sequence order inwhich the storage commands were received based on a characteristic ofthe storage commands. As described above with regard to the I/O journalfilter 282, certain orders of storage commands may have a data spaceand/or time speed benefit for a data store 48. The order module 904 mayadjust an order, reorder, group, and/or rearrange storage commands in anexecution queue 314, in a volatile memory 52, in another buffer, or thelike so that the commands are executed in the adjusted or rearrangedorder. In embodiments where the volatile memory 52, the solid-statestorage device 54, and/or the hard disk drive 56 of a storage applianceor other data store 48 are used as a write combine buffer, the ordermodule 904 may cooperate with the receiver module 902, the buffer module906, and/or the journal module 908 to store data of the write commandsin an adjusted order in a write combine buffer of the storage applianceor other data store 48.

In one embodiment, the order module 904 adjusts an order, reorders,and/or groups storage commands based on different storage volumes forthe storage commands. For example, the order module 904 may adjust anorder of write commands so that write commands directed to a commonstorage volume are grouped together. As used herein, storage commandsare grouped in an order if the storage commands and/or associated datahave a predefined relationship in the order. For example, two storagecommands may be grouped, in various embodiments, if the storage commandsare adjacent in an order, if the storage commands are within apredefined number of storage commands in an order, if the storagecommands or associated data are within the same logical or physical unitin an order (e.g., a logical or physical page), or the like.

Grouping or ordering storage commands and/or associated data by storagevolume, in certain embodiments, may have a data space and/or time speedbenefit. For example, the destage module 910 may destage data by storagevolume. Without the order module 904, the destage module 910 mayotherwise make multiple passes to gather data from a storage volume fordestaging. By ordering received data of write commands (e.g., IOBs,write requests, or other storage commands) by storage volume, the ordermodule 904, in certain embodiments, may reduce a number of passes oriterations the destage module 910 takes to destage data, may makedestaging faster, more efficient, or the like. Further, storage clientsor other users 34, 36 may access data by storage volume, and groupingstorage commands and/or associated data by storage volume may allow adata store 48 to more efficiently provide access by storage volume.

The order module 904, in certain embodiments, adjusts an order orreorders storage commands based on different snapshots, differentversions of a snapshot, and/or different layers of a snapshot, withwhich storage commands are associated. As described above with regard tosnapshots, different snapshots, different versions and/or layers ofsnapshots, or the like may be associated with different time periods forthe same data, storage volume, logical address range, or the like. Theorder module 904 may adjust an order of write commands so that writecommands directed to a common snapshot and/or snapshot version aregrouped together. The order module 904, in one embodiment, by groupingor ordering storage commands and/or associated data by snapshots and/orsnapshot versions, may provide a data space and/or time speed benefit.Storage clients or other users 34, 36 may access data within the samesnapshot or snapshot version, the destage module 910 may destage date bysnapshot and/or by snapshot version, or the like, one or more of whichmay be more efficient if the order module 904 groups, orders, and/orrearranges storage commands or associated data by snapshot and/or bysnapshot version.

In one embodiment, the order module 904 reorders and/or adjusts an orderof storage commands prior to the storage commands or associated databeing recorded in a journal 340. For example, the order module 904 mayreorder and/or adjust an order of storage commands in a volatile memory52, an execution queue 314, or other buffer, may dynamically reorderstorage commands as they're being sent or written to a journal 340, orthe like. Storage commands and/or associated data, in one embodiment,may be stored in a journal 340 preserved in one or more solid-statestorage devices 54 or other non-volatile storage media in an orderdetermined by the order module 904. In other embodiments, the ordermodule 904 may reorder storage commands and/or associated data betweenanother two tiers (e.g., for data being destaged or moved between an SSD54 and SAS 56, between an SAS 56 and a backup server 62 or cloud storageprovider 64, or between other tiers).

The order module 904, in one embodiment, reorders or groups storagecommands and/or associated data based on multiple factors. For example,the order module 904 may order or group storage commands by storagevolume and within the storage commands for a storage volume may group ororder storage commands by snapshot and/or by snapshot version. In afurther embodiment, within storage commands grouped by storage volumeand/or by snapshot, the order module 904 may group or order data bylogical address (e.g., LBA), or the like. Grouping or ordering storagecommands and/or associated data based on multiple factors, in certainembodiments, may provide greater efficiencies or other benefits thanusing a single factor.

While reordering storage commands (e.g., by storage volume, by snapshot,or the like) the order module 904 may maintain a time order orsequential order in which the storage commands were received within eachstorage volume, snapshot, snapshot version, or the like. Maintaining anorder in which storage commands were received for each storage volume(e.g., the time sequence order described above), while rearrangingstorage commands for different storage volumes, in certain embodiments,may provide consistency of operations for each storage volume, whileproviding the efficiencies or other benefits of rearranging storagecommands.

For example, by grouping storage commands by storage volume, by snapshotand/or snapshot version, or the like, the order module 904 may make itmore likely that data from different write commands for the same storagevolume and/or snapshot will be cached or stored in the same, single pageor other logical or physical unit of the journal 340, allowing the datato be paged or loaded into volatile memory 52 at the same time in thesingle page (e.g., in response to a read request), instead of paging orloading multiple different pages into volatile memory 52. For example,two write commands received by the receiver module 902 with more than apage of data of other write requests between them, may be re-ordered orgrouped and stored in the same, single page. In response to a readrequest, the single page may be loaded or paged into volatile memory 52and read requests for data of the two write commands may be satisfiedfrom the single page in memory 52. In this manner, a read request forone block of data in a page of the journal 340 may cause the entire pageto be loaded into volatile memory 52, where other blocks from the samepage may be likely to be read because the order module 904 has groupedthe data based on storage volume, snapshot and/or snapshot version, orthe like. By providing spatial locality for data with similarcharacteristics (e.g., similar storage volume, similar snapshot orsnapshot version, or the like), the order module 904 may provide moreefficient paging or other data access to data in a journal 340.

In one embodiment, the buffer module 906 is configured to store orbuffer storage commands and/or associated data. The buffer module 906may store or buffer storage commands and/or associated data in volatilememory (e.g., the volatile memory 52, an execution queue 314, volatilememory of a computing device 34, 36, 38, 62, 64, or the like). Thebuffer module 906, in one embodiment, may store or buffer storagecommands and/or associated data between elements, at an input, and/or atan output of the filter stack 132. In a further embodiment, the buffermodule 906 may store or buffer storage commands and/or associated databetween tiers 22, 26, 24, 30, 28, 32 of a networked computer system 20,or the like.

The buffer module 906, in certain embodiments, stores or buffers storagecommands and/or associated data in an order determined by the ordermodule 304. The order module 304 may reorder storage commands within abuffer of the buffer module 906, as storage commands are being copiedinto a buffer of the buffer module 906, as storage commands are beingcopied out of a buffer of the buffer module 906, or the like. In oneembodiment, the buffer module 906 executes storage commands in anadjusted order from the order module 904 by storing or buffering thestorage commands in the adjusted order. In a further embodiment, thebuffer module 906 buffers storage commands and/or associated data forrecording or storing in a journal 340.

The buffer module 906, in one embodiment, may determine when to write,copy, destage, and/or move data from a buffer to a non-volatile memorymedia (e.g., a journal 340, a solid-state device 54, a hard disk drive56, or the like). For example, the buffer module 906 may write data inresponse to receiving or buffering a predefined amount of data, fillinga buffer, filling a predefined portion of a buffer, or the like. Thebuffer module 906, in certain embodiments, may determine a frequencywith which data is written from a buffer to a non-volatile storagedevice (e.g., a journal 340, a data store 48, a solid-state storagedevice 54, a hard disk drive 56, a backup server 62, a cloud storageprovider 64, or the like). For example, in one embodiment, the buffermodule 906 may increase a frequency with which data is written from abuffer (e.g., a write buffer) in response to a rate at which storagerequests (e.g., write requests) are received decreasing, may decreasethe frequency in response to the rate increasing, or the like.

By writing data from a buffer more frequently when the buffer is fillingmore slowly (e.g., as write requests are received less frequently), thebuffer module 906 may ensure that a latency is minimized, does not fallbelow a latency threshold, satisfies a latency threshold, or the like.Otherwise, in certain embodiments, latency for the buffered storagecommands may increase when few storage commands are being received,while waiting for a buffer to fill or the like. The buffer module 906may force a buffer to flush, even before the buffer is full, to maintaina certain throughput, minimize a latency, satisfy a latency threshold,or the like. The latency of a write command, in certain embodiments, maybe measured as a time between sending or receiving the write command andacknowledging completion of the write command. The buffer module 906 maydefine a frequency of writing or flushing data from a write buffer sothat a latency for acknowledging completion of multiple, buffered, writerequests satisfies a latency threshold, or the like.

If storage commands are received more frequently, the buffer module 906may decrease a frequency with which the buffer is emptied or flushed(e.g., data is written from the buffer to a non-volatile storagedevice), allowing more data to be buffered or gathered at a time whilestorage commands are being received. It may be counter intuitive toincrease a frequency of writing data from a write buffer in response toa rate of write requests decreasing and to decrease the frequency inresponse to a rate of write requests increasing. However, the buffermodule 906 may manage a frequency of writing or flushing data of a writebuffer in this manner to maximize the benefits of combining writecommands in a buffer (e.g., a write combine buffer as described above)without introducing an unacceptable amount of latency.

The buffer module 906, in certain embodiments, may use multiple timers,multiple timer stages, or the like with different time periods todetermine when to flush a buffer, write data from a buffer, or the like.For example, the buffer module 906, in one embodiment, may use a twostage timer, two timers, or the like. The buffer module 906, may reset afirst, shorter timer (e.g., wait longer to flush a buffer) if a storagerequest, a predefined type of storage request (e.g., a write request),or the like is received for the associated buffer before the first timerexpires. If no storage request, no storage request of a predefined type(e.g., a write request) has been received during the first timer (e.g.,since the first timer was started or reset), the buffer module 906 mayflush the buffer (e.g., write data of the buffer to a differentlocation, to a non-volatile storage device, or the like). In thismanner, if storage requests are being received, the buffer module 906may wait to gather more storage requests before flushing the buffer,executing the storage requests, or the like.

The buffer module 906, in one embodiment, may use a second timer, thatis longer than the first timer, as a fallback or safeguard, and mayflush the buffer (e.g., write data of the buffer to another location, toa non-volatile storage device, or the like) when the second timerexpires, regardless of whether or not storage requests have beenreceived during the second timer. The buffer module 906, by using thesecond timer, with a longer time period or duration than the firsttimer, in certain embodiments, may ensure that the buffer is flushed atleast as often as the period of the second timer. In this manner, thebuffer module 906 may buffer storage commands, data of storage commands,or the like before storing the data in a different location (e.g., ajournal 340, a data store 48, a memory 52, a solid-state storage device54, a hard disk drive 56, or the like) in response to a first timerexpiring without receiving a subsequent storage command, a second timerexpiring, or the like. In other embodiments, the buffer module 906 mayuse a different method to manage a frequency of destaging or flushingdata from a buffer.

The buffer module 906, in certain embodiments, may dynamically adjust orchange a length or period for the first timer and/or the second timer.For example, the buffer module 906 may increase a time period of thefirst timer based on an amount of data in the write buffer, increase atime period of the first timer based on the rate of write requests,decrease the time period of the first timer in response to determiningthat no write requests have been received since the first timer was set,adjust a time period for a timer based on a speed (e.g., I/O operationsper second (IOPS)) of an SSD 54 (e.g., decrease a time period of thefirst and/or second timer for a faster SSD 54), or follow one or moreother adjustment rules for the first timer and/or the second timer.

In one embodiment, the journal module 908 may be substantially similarto the I/O journal filter 282 described above. In certain embodiments,the journal module 908 may record or store storage commands, associateddata and/or metadata, or the like in an order determined by the ordermodule 904, as described above. The journal module 908 may executestorage commands in an adjusted order, in one embodiment, by recordingor storing the storage commands in a journal 340 in the adjusted order.The journal module 908, in various embodiments, may store or recordstorage commands or associated data for multiple storage volumes,multiple snapshots, multiple versions of a snapshot, or the like.

In one embodiment, the destage module 910 is substantially similar tothe destage filter 370 described above. The destage module 910, incertain embodiments, is configured to destage, write, clean, copy, ormove data from a journal 340 to a non-volatile storage device (e.g., astorage volume, a data store 48, a solid-state storage device 54, a harddisk drive 56, a backup server 62, a cloud storage provider 64, oranother backing store). The destage module 910, in one embodiment,destages or writes data based on or according to an order from the ordermodule 904. For example, the journal module 908 may store storagecommands and/or associated data in the order from the order module 904,the order module 904 may reorder storage commands and/or associated datafrom the journal 340, or the like.

The destage module 910, in certain embodiments, may destage or writedata from a single journal 340 to multiple storage volumes, multiplesnapshots, multiple snapshot versions, or the like. In one embodiment,the order module 904 may group or order storage commands in a journal340 by storage volume, by snapshots, by snapshot version, or the likeand the destage module 910 may destage or write back data substantiallyin the order from the journal 340. In a further embodiment, the destagemodule 910 may scan the journal 340 to combine data and/or storagecommands for the same storage volume, the same snapshot, and/or the samesnapshot version from different locations within the journal 340, whiledestaging or writing data for each individual storage volume, snapshot,and/or snapshot version in the order from the order module 904.

The destage module 910, in one embodiment, stored, writes, or destagesdata from a journal 340 to a non-volatile memory device by executing thestorage commands recorded in the journal 340 on the non-volatile memorydevice. For example, the destage module 910 may execute a sequence ofwrite commands, write requests, or the like from a journal 340 so thatthe data of the write commands or requests is stored in a storage volumeassociated with the write commands or requests. The destage module 910,in certain embodiments, may execute storage commands from a journal 340in an order which the order module 904 determined for the storagecommands (e.g., an adjusted order, a reordering, or the like).

In one embodiment, the region management module 912 is configured tomanage what ratio or percentage of a journal 340, of a data store 48, ofa solid-state storage device 54, of a hard disk drive 56, or the like isused to store different types of data (e.g., read data and write data,mirrored data and non-mirrored data, or the like). For example, incertain embodiments, as described above, write data, write requests, orthe like are mirrored (e.g., a copy of the data is maintained) inmultiple journals 340 of a storage array or data store 48 (e.g.,mirrored in a first journal 340 maintained in a first SSD 54A and in asecond journal 340 maintained in a second SSD 54B, or the like). Theregion management module 912 may mirror or maintain a copy of cachedwrite data at least until the destage module 910 destages, cleans, orotherwise writes the data to its destination (e.g., a storage volume ofa hard disk drive 56), to provide redundancy or the like. The regionmanagement module 912, in a further embodiment, may cache read datawithout mirroring the cached read data, since the read data is alreadystored in its intended location (e.g., a storage volume, a hard diskdrive 56, or the like). For example, in response to a read miss for ablock of data, a range of data, or the like, the journal module 908 mayread the data and store the data back in the journal 340, to satisfy theread request causing the read miss or the like.

The region management module 912, in certain embodiments, maydynamically adjust a boundary between mirrored, cached write data andnon-mirrored, cached read data, may assign or adjust a storage capacityfor mirrored, cached write data and/or for non-mirrored, cached readdata, or may otherwise allocate capacity or room in one or more journals340. The region management module 912 may base a boundary or storagecapacity for mirrored and non-mirrored data, for read data and writedata, or for other types of cached data based on storage requestsreceived for the data, based on a current workload, based on a currentuse case, based on a ratio of received write commands and received readcommands, a rate of receiving write commands, a rate of receiving readcommands, or the like.

For example, the region management module 912 may increase a storagecapacity for cached, mirrored, write data in response to a writerequest, in response to a threshold number of write requests, inresponse to more write requests than read requests, or the like, mayincrease a storage capacity for cached, non-mirrored, read data inresponse to a read request, in response to a threshold number of readrequests, in response to more read requests than write requests, or thelike. By dynamically adjusting a storage capacity for mirrored datacompared to non-mirrored data, in certain embodiments, the regionmanagement module 912 may allow an optimal and/or efficient use ofstorage capacity, by reducing an amount of mirrored data when possible,allowing twice the amount of non-mirrored data to be stored in itsplace, or the like.

FIG. 10 depicts one embodiment of a system 920 for journal management.In the depicted embodiment, one or more of the initiators 38A-38C aresending block command packets to the primary data storage system 28 thatrelate to the three different storage volumes, volume 01, volume 02, andvolume 03. Each of the block command packets have been processed togenerate an IOB, such as IOB 182.

The buffer module 906 places each IOB that is received into the inputqueue 300. The order module 904 processes each of the IOBs in the queue300 in the order that the IOB was received in the queue 300 (e.g., anoriginal time sequence order). In the depicted embodiment, the ordermodule 904 groups or reorders IOBs from the queue 300 according to thestorage volume to which an IOB belongs, based on a VolID field 222 ofthe IOB or the like. In a further embodiment, the order module 904 maygroup or reorder IOBs from the queue 300 according to a snapshot orsnapshot version to which an IOB belongs, based on a LayerID field 242of the IOB or the like, may order IOBs based on both a storage volumeand a snapshot or snapshot version, and/or may order IOBs based onanother factor, attribute, or characteristic of the IOBs. In thedepicted embodiment, the order module 904 groups or orders the IOBs intoa first grouping 922 of IOBs for storage volume 01, a second grouping924 of IOBs for storage volume 02, and a third grouping 926 of IOBs forstorage volume 03, each within the execution queue 314.

The journal module 908, in the depicted embodiment, records or writesIOBs from the execution queue 314 to a first journal 340 a maintained ina first solid-state storage device 54 a and to a second journal 340 bmaintained in a second solid-state storage device 54 b, so that the IOBsand included data of write commands from the one or more initiators38A-38C is mirrored to provide redundancy. The destage module 910, inthe depicted embodiment, writes, cleans, copies, moves, and/or destagesdata from the journals 340 a-b to one or more hard disk drives 56. Thedestage module 910, in certain embodiments, may leave clean, destageddata in at least one of the journals 340 a-b to service read requestsfrom the journals 340 a-b (e.g., from a journal page 342 paged intovolatile memory 52A or the like).

The region management module 912, in the depicted embodiment,dynamically sets a boundary 928 between mirrored write data cached inthe journals 340 a-b and non-mirrored read data cached in the journals340 a-b. For example, the region management module 912 may adjust theboundary 928 and allotted storage capacities of the journals 340 a-band/or the solid-state storage devices 54 a-b by evicting mirrored writedata from the journals 340 a-b (e.g., after the data has beendestaged/cleaned), by evicting non-mirrored read data from the journals340 a-b and/or the solid-state storage devices 54 a-b, by loading orwriting additional non-mirrored read data into the journals 340 a-band/or the solid-state storage devices 54 a-b, or the like.

In the depicted embodiment, in response to a read miss for the journals340 a-b (e.g., data of a read request not being stored in one of thejournals 340 a-b), the region management module 912 places one or moreIOBs for the read request into the input queue 300, so that the data ofthe read request is stored in at least one of the journals 340 a-b. Inthe depicted embodiment, because read data is already stored in the harddisk drive 56 or another backing store, the journal module 908 isconfigured to store data of read commands in a single journal 340 a or340 b, instead of mirroring the data as it would for data of a writecommand. For example, the journal module 908 may determine whether anIOB is for a read command or a write command based on a Command field230 for the IOB, and may mirror IOBs for write commands withoutmirroring IOBs for read commands. In this manner, the region managementmodule 912 may dynamically adjust a boundary 928 or ratio of mirroredwrite data to non-mirrored read data, as described above.

Because, in the depicted embodiment, cached read data is not mirroredwhile cached write data is mirrored, a total amount of unique datacached in the journals 340 a-b increases in response to the regionmanagement module 912 decreasing the storage capacity used for storingmirrored write data and increasing the storage capacity used for storingnon-mirrored read data. For example, if one mirrored journal page 342 ofmirrored write data is evicted from each of the journals 340 a-b, theresulting storage capacity will allow two journal pages 342 ofnon-mirrored read data to be cached in its place, resulting in anincrease in an amount of unique data cached in the journals 340 a-b. Inthis manner, the region management module 912, in one embodiment, mayprovide the advantages of redundancy for the mirrored write data whileproviding an increase in storage capacity for the non-mirrored readdata, and may dynamically adjust each based on a use case or otherfactor.

FIG. 11 depicts one embodiment of a method 1000 for journal management.The method 1000 begins and the receiver module 902 receives 1002 aplurality of storage commands (e.g., storage requests, IOBs, or otherI/O commands) for different storage volumes, for different snapshots,for different layers or versions (e.g., time periods) of a snapshot, orthe like. The order module 904 adjusts 1004 an order of the received1002 storage commands. In one embodiment, the order module 904 adjusts1004 an order for or reorders the storage commands so that storagecommands for a storage volume are grouped together. In a furtherembodiment, the order module 904 adjusts 1004 an order for or reordersthe storage commands based on which layer or version of a snapshot thestorage commands are associated. One or more of the buffer module 906,the journal module 908, and the destage module 910 executes 1006 thereceived 1002 storage commands in the adjusted 1004 order (e.g., thebuffer module 906 buffers or lists the storage commands in the adjusted1004 order, the journal module 908 records the storage commands and/ordata of the storage commands in a journal 340, the destage module 910writes data of the storage commands from a journal 340 to a non-volatilestorage device 54, 56, or the like) and the method 1000 ends.

FIG. 12 depicts a further embodiment of a method 1100 for journalmanagement. The method 1100 begins and the buffer module 906 starts 1102a first timer and a second timer. In certain embodiments, the secondtimer has a longer time period than the first timer. The buffer module906 determines 1104 when the first timer has expired. When the buffermodule 906 determines 1104 that the first timer has expired, the buffermodule 906 determines 1106 whether any write requests have been receivedsince the first timer started 1102. If the buffer module 906 determines1106 that at least one write request has been received, the buffermodule 906 resets 1108 the first timer. If the buffer module 906determines 1106 that no write requests have been received since thefirst timer started 1102, the buffer module 906 writes 1112 data from abuffer (e.g., a volatile memory 52, an execution queue 314, a writebuffer, a write combine buffer, or the like) to non-volatile storage,such as a journal 340, one or more non-volatile media 54 of a storagedevice 48 (e.g., solid-state storage 54, a hard disk drive 56), or thelike.

The buffer module 906 determines 1110 when the second timer has expired.When the buffer module 906 determines 1110 that the second timer hasexpired, the buffer module 906 writes 1112 data from the buffer tonon-volatile storage. If the buffer module 906 determines 1104, 1110that neither the first nor the second timer have expired, the buffermodule 906 continues to wait and/or monitor the first and second timers,and the method 1100 continues.

FIG. 13 depicts another embodiment of a method 1200 for journalmanagement. The region management module 912 mirrors 1202 cached writedata in one or more journals 340. The journals 340 may be stored in oneor more of a data store 48A, 48B; an SSD 54A, 54B; a hard disk drive56A, 56B; a volatile memory 48A, 48B; or the like. The region managementmodule 912 stores 1204 cached read data in the one or more journals 340without mirroring the cached read data. The region management module 912adjusts 1206 a ratio of storage capacity of the one or more journals 340used for storing 1202 mirrored cached write data to storage capacity ofthe one or more journals 340 used for storing 1204 non-mirrored cachedread data based on storage requests for data of the one or more journals340 or the like and the method 1200 ends.

A means for mirroring cached write data in one or more journals 340, invarious embodiments, may include a management module 900, a regionmanagement module 912, a journal module 908, a storage processor 46, adata store 48, a solid-state storage device 54, a disk drive 56, adevice driver, a memory controller, a storage controller, other logichardware, and/or other executable code stored on a computer readablestorage medium. Other embodiments may include similar or equivalentmeans for mirroring cached write data in one or more journals 340.

A means for storing cached read data in one or more journals 340 withoutmirroring the cached read data, in various embodiments, may include amanagement module 900, a region management module 912, a journal module908, a storage processor 46, a data store 48, a solid-state storagedevice 54, a disk drive 56, a device driver, a memory controller, astorage controller, other logic hardware, and/or other executable codestored on a computer readable storage medium. Other embodiments mayinclude similar or equivalent means for storing cached read data in oneor more journals 340 without mirroring the cached read data.

A means for adjusting a ratio of storage capacity of one or morejournals 340 used for storing mirrored cached write data to storagecapacity of the one or more journals 340 used for storing non-mirroredcached read data, in various embodiments, may include a managementmodule 900, a region management module 912, a journal module 908, astorage processor 46, a data store 48, a solid-state storage device 54,a disk drive 56, a device driver, a memory controller, a storagecontroller, other logic hardware, and/or other executable code stored ona computer readable storage medium. Other embodiments may includesimilar or equivalent means for adjusting a ratio of storage capacity ofone or more journals 340 used for storing mirrored cached write data tostorage capacity of the one or more journals 340 used for storingnon-mirrored cached read data.

The present disclosure may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the disclosure is, therefore,indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. A computer program product comprising a computerreadable storage medium storing computer usable program code executableto perform operations, the operations comprising: monitoring a rate atwhich write requests are received; increasing a frequency of writingdata from a write buffer to a non-volatile storage medium in response toa rate of write requests decreasing; and decreasing the frequency ofwriting data from the write buffer to the non-volatile storage medium inresponse to the rate of write requests increasing.
 2. The computerprogram product of claim 1, wherein decreasing the frequency comprises:resetting a first timer for the write buffer in response to determiningthat one or more write requests have been received since the first timerwas set; and writing the data from the write buffer to the non-volatilestorage medium in response to expiration of a second timer, the secondtimer having a longer time period than the first timer.
 3. The computerprogram product of claim 2, wherein increasing the frequency compriseswriting data from the write buffer to the non-volatile storage medium inresponse to determining that no write requests have been received sincethe first timer was set.
 4. The computer program product of claim 2,wherein the operations further comprise one or more of increasing a timeperiod of the first timer based on an amount of data in the writebuffer, increasing a time period of the first timer based on the rate ofwrite requests, and decreasing the time period of the first timer inresponse to determining that no write requests have been received sincethe first timer was set.
 5. The computer program product of claim 1,wherein the data from the write buffer is written to a journal datastructure maintained in the non-volatile storage medium.
 6. The computerprogram product of claim 1, wherein the write buffer comprises a writecombine buffer such that the data written to the non-volatile storagemedium comprises data of multiple write requests, the frequency ofwriting data from the write buffer defined such that a latency foracknowledging completion of the multiple write requests satisfies alatency threshold.
 7. An apparatus comprising: means for mirroringcached write data in one or more journals; means for caching read datain at least one journal without mirroring the cached read data; andmeans for adjusting a ratio of storage capacity of the one or morejournals used for storing mirrored cached write data to storage capacityof the one or more journals used for storing non-mirrored cached readdata based on storage requests for data of the one or more journals. 8.The apparatus of claim 7, wherein the means for adjusting the ratiodecreases the storage capacity of the one or more journals used forstoring mirrored cached write data and increases the storage capacity ofthe one or more journals used for storing non-mirrored cached read datain response to receiving more read requests than write requests.
 9. Theapparatus of claim 8, wherein an amount of unique data cached in the oneor more journals increases in response to decreasing the storagecapacity used for storing mirrored cached write data and increasing thestorage capacity used for storing non-mirrored cached read data.
 10. Theapparatus of claim 7, wherein the one or more journals are preserved innon-volatile storage media associated with at least two storageprocessors, the cached write data mirrored in non-volatile storage mediaassociated with each of the at least two storage processors.